feat(db): solver + setup templates + cables/bundles store

Migration 004:
- setup_templates + setup_template_devices + setup_template_requirements
- 3 built-in templates seeded: Living Room (TV+Soundbar+ChromeCast,
  2× HDMI), Home Office (PC+Screen+Keyboard+Mouse, 1× HDMI + 2× USB),
  Server Rack (NAS+Switch+fritz, 2× RJ45).

Cables store (cables.go):
- CRUD with endpoint validation (port|device|io exactly-one, project-
  scoped). Tx-aware: validateEndpointEx + assertCableTypeEx avoid
  deadlocks when the solver Apply tx holds the MaxOpenConns(1) connection.

Bundles store (bundles.go):
- CRUD with cable_ids replacement on PATCH. createBundle(ex, …, ownTx)
  inherits the caller's tx for solver-internal use; returns a locally-
  constructed Bundle when ownTx=false (re-fetching via s.db would
  deadlock).

Solver (solver.go) implements design v4.1 §5b.2 exactly:
- Pre-fetch devices/ports/cables/requirements/bundles.
- Reserve ports used by manual cables (auto=0) so the solver can't
  reuse them.
- For each requirement (must_connect DESC, id ASC):
    * Resolve cable type: preferred, or T = port-types(from) ∩
      port-types(to). |T|==0 → unsatisfied "no compat type"; |T|>1 →
      "ambiguous"; |T|==1 → that one.
    * Pick lowest-id free port on each side. None → unsatisfied with
      WhichSide hint + cable-type name.
- Endpoint-pair bundle: ≥2 staged cables between the same device pair
  → auto bundle.
- Diff against existing auto cables by (type_id, MIN(from,to), MAX(from,to))
  signature. Matched = kept; new = added; orphans = removed.
- Preview returns the diff without writing; Apply runs in a single tx
  that wipes auto bundles, deletes orphan auto cables, inserts new
  ones, and rebuilds bundles.
- PortsAndResolve: combo helper for the inspector quick-fix —
  inserts a port + re-runs Solve.

Setup-templates store (setup_templates.go):
- List/Get with hydrated devices + requirements.
- ApplyTemplate(projectID, templateID, opts) seeds devices + requirements
  in one tx. Per-device name overrides + opt-out. Name collisions skip
  the device (skipped_devices); requirements whose endpoints both fail
  are also skipped (requirements_skipped). UNIQUE-collision on an
  existing requirement is non-fatal; logged in requirements_skipped.

Snapshot: cables + bundles fields tightened to []Cable / []Bundle and
populated from the store.

11 new tests (solver_test.go), all green with -race:
- Basic NAS↔Switch (RJ45) → 1 cable, auto=true
- Ambiguous cable type → unsatisfied
- No free port → unsatisfied with side hint
- Preview doesn't write
- Apply then re-apply → idempotent (kept=N, added=0)
- Manual cable reserves its port → solver can't claim it
- ApplyTemplate Living Room → 3 devices + 2 requirements + 7 ports
  (from the device-type port seeder)
- Home Office template then Solve → 3 cables, 0 unsatisfied
- Name-collision pre-existing device → skipped + req-pair skipped

internal/db/bundles.go

@@ -0,0 +1,222 @@
+package db
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// BundleCreate is the create-shape: a name + the cable IDs to include.
+// Auto=true means the solver created the bundle; user-created bundles
+// stay auto=0 and survive a re-solve.
+type BundleCreate struct {
+	Name     string
+	CableIDs []int64
+	Auto     bool
+}
+
+type BundleUpdate struct {
+	Name     *string
+	CableIDs *[]int64
+}
+
+// CreateBundle inserts a bundle + its cable_bundle rows in one tx.
+func (s *Store) CreateBundle(projectID int64, b BundleCreate) (*Bundle, error) {
+	return s.createBundle(s.db, projectID, b, true)
+}
+
+func (s *Store) createBundle(ex execer, projectID int64, b BundleCreate, ownTx bool) (*Bundle, error) {
+	name := strings.TrimSpace(b.Name)
+	if name == "" {
+		return nil, fmt.Errorf("%w: name is required", ErrInvalidInput)
+	}
+	// When the caller already holds a tx (ownTx=false), do all validation
+	// against `ex` (the tx executor) — calling Store methods that hit
+	// s.db would deadlock against the connection the tx is holding under
+	// MaxOpenConns(1).
+	for _, cid := range b.CableIDs {
+		if _, err := s.getCableTx(ex, projectID, cid); err != nil {
+			if errors.Is(err, ErrNotFound) {
+				return nil, fmt.Errorf("%w: cable_id %d not in project", ErrInvalidInput, cid)
+			}
+			return nil, err
+		}
+	}
+	autoInt := 0
+	if b.Auto {
+		autoInt = 1
+	}
+
+	var tx *sql.Tx
+	var err error
+	useEx := ex
+	if ownTx {
+		tx, err = s.db.Begin()
+		if err != nil {
+			return nil, err
+		}
+		defer tx.Rollback()
+		useEx = tx
+	}
+	res, err := useEx.Exec(
+		`INSERT INTO bundles (project_id, name, auto) VALUES (?, ?, ?)`,
+		projectID, name, autoInt,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	id, _ := res.LastInsertId()
+	for _, cid := range b.CableIDs {
+		if _, err := useEx.Exec(
+			`INSERT INTO bundle_cables (bundle_id, cable_id) VALUES (?, ?)`, id, cid,
+		); err != nil {
+			return nil, mapWriteErr(err)
+		}
+	}
+	if ownTx {
+		if err := tx.Commit(); err != nil {
+			return nil, err
+		}
+		return s.GetBundle(projectID, id)
+	}
+	// In tx-inheriting mode, build the response struct locally — the
+	// caller will re-fetch via GetBundle after commit if it needs more.
+	out := &Bundle{
+		ID: id, ProjectID: projectID, Name: name, Auto: b.Auto, CableIDs: append([]int64(nil), b.CableIDs...),
+	}
+	return out, nil
+}
+
+func (s *Store) GetBundle(projectID, id int64) (*Bundle, error) {
+	var b Bundle
+	var autoInt int
+	err := s.db.QueryRow(
+		`SELECT id, project_id, name, auto, created_at, updated_at
+		 FROM bundles WHERE id = ? AND project_id = ?`, id, projectID,
+	).Scan(&b.ID, &b.ProjectID, &b.Name, &autoInt, &b.CreatedAt, &b.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	b.Auto = autoInt != 0
+	ids, err := s.bundleCableIDs(id)
+	if err != nil {
+		return nil, err
+	}
+	b.CableIDs = ids
+	return &b, nil
+}
+
+func (s *Store) bundleCableIDs(bundleID int64) ([]int64, error) {
+	rows, err := s.db.Query(
+		`SELECT cable_id FROM bundle_cables WHERE bundle_id = ? ORDER BY cable_id`, bundleID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []int64{}
+	for rows.Next() {
+		var v int64
+		if err := rows.Scan(&v); err != nil {
+			return nil, err
+		}
+		out = append(out, v)
+	}
+	return out, rows.Err()
+}
+
+// ListBundles returns every bundle in a project, ordered by id.
+func (s *Store) ListBundles(projectID int64) ([]Bundle, error) {
+	rows, err := s.db.Query(
+		`SELECT id, project_id, name, auto, created_at, updated_at
+		 FROM bundles WHERE project_id = ? ORDER BY id`, projectID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []Bundle{}
+	for rows.Next() {
+		var b Bundle
+		var autoInt int
+		if err := rows.Scan(&b.ID, &b.ProjectID, &b.Name, &autoInt,
+			&b.CreatedAt, &b.UpdatedAt); err != nil {
+			return nil, err
+		}
+		b.Auto = autoInt != 0
+		out = append(out, b)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	for i := range out {
+		ids, err := s.bundleCableIDs(out[i].ID)
+		if err != nil {
+			return nil, err
+		}
+		out[i].CableIDs = ids
+	}
+	return out, nil
+}
+
+// UpdateBundle: name + cable set are mutable. Replacing cables wipes
+// bundle_cables and re-inserts in one tx.
+func (s *Store) UpdateBundle(projectID, id int64, u BundleUpdate) (*Bundle, error) {
+	cur, err := s.GetBundle(projectID, id)
+	if err != nil {
+		return nil, err
+	}
+	if u.Name != nil {
+		v := strings.TrimSpace(*u.Name)
+		if v == "" {
+			return nil, fmt.Errorf("%w: name cannot be empty", ErrInvalidInput)
+		}
+		cur.Name = v
+	}
+	tx, err := s.db.Begin()
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+	if _, err := tx.Exec(
+		`UPDATE bundles SET name = ?, updated_at = datetime('now') WHERE id = ?`,
+		cur.Name, id,
+	); err != nil {
+		return nil, mapWriteErr(err)
+	}
+	if u.CableIDs != nil {
+		if _, err := tx.Exec(`DELETE FROM bundle_cables WHERE bundle_id = ?`, id); err != nil {
+			return nil, err
+		}
+		for _, cid := range *u.CableIDs {
+			if _, err := s.getCableTx(tx, projectID, cid); err != nil {
+				return nil, fmt.Errorf("%w: cable_id %d not in project", ErrInvalidInput, cid)
+			}
+			if _, err := tx.Exec(
+				`INSERT INTO bundle_cables (bundle_id, cable_id) VALUES (?, ?)`, id, cid,
+			); err != nil {
+				return nil, mapWriteErr(err)
+			}
+		}
+	}
+	if err := tx.Commit(); err != nil {
+		return nil, err
+	}
+	return s.GetBundle(projectID, id)
+}
+
+func (s *Store) DeleteBundle(projectID, id int64) error {
+	if _, err := s.GetBundle(projectID, id); err != nil {
+		return err
+	}
+	if _, err := s.db.Exec(
+		`DELETE FROM bundles WHERE id = ? AND project_id = ?`, id, projectID,
+	); err != nil {
+		return err
+	}
+	return nil
+}