feat(projects): t-paliad-232 Verfahrenstyp picker + Schriftsätze CTA

Two-part fix from m's 2026-05-21 finding that the Schriftsätze tab
told users "Bitte zuerst einen Verfahrenstyp setzen" while the
project form had no field to set it. The `proceeding_type_id`
column was already on `paliad.projects` and accepted by the API.

  Part 1 — Verfahrenstyp picker on the case-fields block

    * frontend/src/components/ProjectFormFields.tsx — new optional
      <select id="project-proceeding-type-id"> rendered between
      Aktenzeichen and Mandantenrolle inside the type=case block.
      First option is "(nicht gesetzt)" / "(unset)".
    * frontend/src/client/project-form.ts — shared
      loadProceedingTypes() + populateProceedingTypeSelect()
      helpers. Options sorted by `code` (de.* → dpma.* → epa.* →
      upc.*). readPayload sends `proceeding_type_id` only when the
      user picked a value; prefillForm restores the saved id via
      dataset.preselect to survive the async populate race.
    * frontend/src/client/projects-new.ts — kicks off populate on
      DOMContentLoaded.
    * frontend/src/client/projects-detail.ts — edit-modal preload
      now awaits populate; the local loadProceedingTypes duplicate
      (used by the counterclaim modal) is replaced by the shared
      helper so both surfaces hit the same cache.

  Part 2 — Actionable empty-state on the Schriftsätze tab

    * frontend/src/projects-detail.tsx — the static <p> empty-state
      becomes a div with a "Projekt bearbeiten" button.
    * frontend/src/client/projects-detail.ts — openEditModal now
      accepts an optional focusFieldID; the new
      #project-submissions-edit-cta click handler calls it with
      "project-proceeding-type-id" so the picker is scrolled into
      view and focused right after the modal opens.

  i18n: new keys projects.field.proceeding_type{,.unset,.hint} and
  projects.detail.submissions.empty.no_proceeding.cta; reworded
  no_proceeding copy to match the new "edit the project" CTA.

  Backend already validates via validateProceedingTypeCategory
  (mig 087/088 fristenrechner-category guard). Added
  TestProjectService_CaseProceedingTypePicker exercising both the
  happy and reject paths through a `case`-typed Create.

Manual test path: open any case project → Edit → the Verfahrenstyp
picker shows below Aktenzeichen → save → the Schriftsätze tab now
lists the submission codes. Clicking the empty-state CTA jumps
straight to the picker.

internal/services/project_service_test.go

@@ -253,3 +253,95 @@ func TestProjectService_InstanceLevel_Roundtrip(t *testing.T) {
 		t.Errorf("want ErrInvalidInput, got %v", err)
 	}
 }
+
+// TestProjectService_CaseProceedingTypePicker covers the t-paliad-232
+// data path for the new project-form Verfahrenstyp picker:
+//
+//  1. Creating a `case`-typed project with a fristenrechner-category
+//     proceeding_type_id round-trips the column.
+//  2. The same code path rejects a non-fristenrechner-category id with
+//     ErrInvalidProceedingTypeCategory (mirror of the guard test above,
+//     this time exercised through a 'case' shape).
+//
+// Skipped when TEST_DATABASE_URL is unset.
+func TestProjectService_CaseProceedingTypePicker(t *testing.T) {
+	url := os.Getenv("TEST_DATABASE_URL")
+	if url == "" {
+		t.Skip("TEST_DATABASE_URL not set — skipping live DB test")
+	}
+	if err := db.ApplyMigrations(url); err != nil {
+		t.Fatalf("apply migrations: %v", err)
+	}
+	pool, err := sqlx.Connect("postgres", url)
+	if err != nil {
+		t.Fatalf("connect: %v", err)
+	}
+	defer pool.Close()
+
+	ctx := context.Background()
+
+	var fristenrechnerID int
+	if err := pool.GetContext(ctx, &fristenrechnerID,
+		`SELECT id FROM paliad.proceeding_types
+		  WHERE category = 'fristenrechner' AND code = $1 AND is_active = true`,
+		CodeUPCInfringement); err != nil {
+		t.Fatalf("look up %s id: %v", CodeUPCInfringement, err)
+	}
+	var nonFristenrechnerID int
+	if err := pool.GetContext(ctx, &nonFristenrechnerID,
+		`SELECT id FROM paliad.proceeding_types
+		  WHERE category <> 'fristenrechner'
+		  ORDER BY id
+		  LIMIT 1`); err != nil {
+		t.Fatalf("look up non-fristenrechner id: %v", err)
+	}
+
+	users := NewUserService(pool)
+	svc := NewProjectService(pool, users)
+
+	userID := uuid.New()
+	cleanup := func() {
+		pool.ExecContext(ctx, `DELETE FROM paliad.projects WHERE created_by = $1`, userID)
+		pool.ExecContext(ctx, `DELETE FROM paliad.users    WHERE id = $1`, userID)
+		pool.ExecContext(ctx, `DELETE FROM auth.users      WHERE id = $1`, userID)
+	}
+	cleanup()
+	defer cleanup()
+
+	if _, err := pool.ExecContext(ctx,
+		`INSERT INTO auth.users (id, email) VALUES ($1, 't-paliad-232-test@hlc.com')`,
+		userID); err != nil {
+		t.Fatalf("seed auth.users: %v", err)
+	}
+	if _, err := pool.ExecContext(ctx,
+		`INSERT INTO paliad.users (id, email, display_name, office, role, lang)
+		 VALUES ($1, 't-paliad-232-test@hlc.com', 'Picker Test', 'munich', 'associate', 'de')`,
+		userID); err != nil {
+		t.Fatalf("seed paliad.users: %v", err)
+	}
+
+	// 1. Case-typed create with a fristenrechner id succeeds.
+	created, err := svc.Create(ctx, userID, CreateProjectInput{
+		Type:             ProjectTypeCase,
+		Title:            "t-paliad-232 — case with proceeding_type_id",
+		ProceedingTypeID: &fristenrechnerID,
+	})
+	if err != nil {
+		t.Fatalf("Create case with fristenrechner id: %v", err)
+	}
+	if created.ProceedingTypeID == nil || *created.ProceedingTypeID != fristenrechnerID {
+		t.Errorf("created proceeding_type_id = %v, want %d", created.ProceedingTypeID, fristenrechnerID)
+	}
+
+	// 2. Case-typed create with a non-fristenrechner id is rejected.
+	_, err = svc.Create(ctx, userID, CreateProjectInput{
+		Type:             ProjectTypeCase,
+		Title:            "t-paliad-232 — case with non-fristenrechner id",
+		ProceedingTypeID: &nonFristenrechnerID,
+	})
+	if err == nil {
+		t.Error("Create case with non-fristenrechner proceeding_type_id should fail, but succeeded")
+	} else if !errors.Is(err, ErrInvalidProceedingTypeCategory) {
+		t.Errorf("expected ErrInvalidProceedingTypeCategory, got %v", err)
+	}
+}