refactor(rename): German→English for backend (tables, types, services, handler files)

t-paliad-025 — Phase 1: backend rename.

Migrations 018+019 rewritten from scratch with English table/column
names throughout. Since v2 schema (018/019) has never been applied to
youpc prod DB, this is a clean replacement — not an ALTER RENAME chain.
Pre-existing German tables (parteien, fristen, termine, dokumente,
akten_events, notizen) are renamed inline in 018 via ALTER TABLE … RENAME
TO alongside the akte_id → project_id column rewrite.

Renames applied:
  projekte            → projects
  projekt_teams       → project_teams
  projekt_events      → project_events (via akten_events → project_events)
  fristen             → deadlines
  termine             → appointments
  parteien            → parties
  notizen             → notes
  dezernate           → departments
  dezernat_mitglieder → department_members
  dokumente           → documents
  can_see_projekt     → can_see_project
  notiz_is_visible    → note_is_visible
  akte_id  / frist_id / termin_id / akten_event_id → project_id /
    deadline_id / appointment_id / project_event_id
  termin_type → appointment_type

Go types + services renamed:
  Projekt / ProjektService / ProjektEvent / ProjektTeamMember
  Frist / FristService / FristWithProjekt
  Termin / TerminService / TerminWithProjekt / TerminType
  Notiz / NotizService / ChecklistInstanceWithProjekt
  Dezernat / DezernatService / DezernatMitglied
  Partei / Parteien / ParteienService

Files renamed (git mv):
  internal/services/{projekt,frist,termin,notiz,dezernat,parteien}_service.go
    → {project,deadline,appointment,note,department,party}_service.go
  internal/handlers/{projekte,fristen,fristen_pages,termine,termine_pages,
    notizen,dezernate,akten_pages,gerichte,glossar,checklisten}.go
    → {projects,deadlines,deadlines_pages,appointments,appointments_pages,
       notes,departments,projects_pages,courts,glossary,checklists}.go
  internal/checklisten/ → internal/checklists/
  internal/db/migrations/018_projekte_v2.* → 018_projects_v2.*
  internal/db/migrations/019_seed_dezernate_from_user_text.*
    → 019_seed_departments_from_user_text.*

User-facing i18n strings (DE/EN labels) stay untouched. Product names
Fristenrechner / Kostenrechner / Gebührentabellen stay German.

Build + vet + tests clean.

cmd/server/main.go

@@ -52,7 +52,7 @@ func main() {
 
 	// DATABASE_URL is optional during the Phase A → Phase D transition. The
 	// existing knowledge-platform features (Kostenrechner, Glossar, etc.) work
-	// without a DB. Akten/Frist endpoints return 503 until DATABASE_URL is set.
+	// without a DB. Akten/Deadline endpoints return 503 until DATABASE_URL is set.
 	dbURL := os.Getenv("DATABASE_URL")
 	var svcBundle *handlers.Services
 	var caldavSvc *services.CalDAVService
@@ -70,9 +70,9 @@ func main() {
 		}
 		holidays := services.NewHolidayService(pool)
 		users := services.NewUserService(pool)
-		projektSvc := services.NewProjektService(pool, users)
+		projektSvc := services.NewProjectService(pool, users)
 		teamSvc := services.NewTeamService(pool, projektSvc)
-		dezernatSvc := services.NewDezernatService(pool, users)
+		dezernatSvc := services.NewDepartmentService(pool, users)
 		rules := services.NewDeadlineRuleService(pool)
 
 		// Phase F: optional CalDAV cipher. If CALDAV_ENCRYPTION_KEY is unset
@@ -89,7 +89,7 @@ func main() {
 			log.Println("CalDAV encryption configured (AES-256-GCM)")
 		}
 
-		terminSvc := services.NewTerminService(pool, projektSvc)
+		terminSvc := services.NewAppointmentService(pool, projektSvc)
 		caldavSvc = services.NewCalDAVService(pool, cipher, terminSvc)
 		// Wire the push hook so user-driven mutations sync to the external
 		// calendar without waiting for the next 60-second tick.
@@ -100,19 +100,19 @@ func main() {
 		reminderSvc := services.NewReminderService(pool, mailSvc, users, baseURL)
 
 		svcBundle = &handlers.Services{
-			Projekt:        projektSvc,
+			Project:        projektSvc,
 			Team:           teamSvc,
 			Dezernat:       dezernatSvc,
-			Parteien:       services.NewParteienService(pool, projektSvc),
-			Frist:          services.NewFristService(pool, projektSvc),
-			Termin:         terminSvc,
+			Parties:       services.NewPartyService(pool, projektSvc),
+			Deadline:          services.NewDeadlineService(pool, projektSvc),
+			Appointment:         terminSvc,
 			CalDAV:         caldavSvc,
 			Rules:          rules,
 			Calculator:     services.NewDeadlineCalculator(holidays),
 			Users:          users,
 			Fristenrechner: services.NewFristenrechnerService(rules, holidays),
 			Dashboard:      services.NewDashboardService(pool, users),
-			Notiz:          services.NewNotizService(pool, projektSvc, terminSvc),
+			Note:          services.NewNoteService(pool, projektSvc, terminSvc),
 			ChecklistInst:  services.NewChecklistInstanceService(pool, projektSvc),
 			Mail:           mailSvc,
 			Invite:         inviteSvc,
@@ -132,7 +132,7 @@ func main() {
 			caldavSvc.Stop()
 		}()
 	} else {
-		log.Println("DATABASE_URL not set — Akten/Frist endpoints will return 503")
+		log.Println("DATABASE_URL not set — Akten/Deadline endpoints will return 503")
 	}
 
 	mux := http.NewServeMux()