feat: add deadline management frontend (Phase 1G)

- Fristen page with list view (sortable, filterable by status/case)
- Calendar view with month navigation and deadline dots
- Deadline calculator page (proceeding type + trigger date = timeline)
- Traffic light urgency: red (overdue), amber (this week), green (OK)
- Backend: GET /api/deadlines (all tenant deadlines), GET /api/proceeding-types
- API client: added patch() method
- Types: DeadlineRule, ProceedingType, CalculatedDeadline, RuleTreeNode

backend/internal/router/router.go

@@ -81,6 +81,7 @@ func New(db *sqlx.DB, authMW *auth.Middleware, cfg *config.Config) http.Handler
 	scoped.HandleFunc("DELETE /api/parties/{partyId}", partyH.Delete)
 
 	// Deadlines
+	scoped.HandleFunc("GET /api/deadlines", deadlineH.ListAll)
 	scoped.HandleFunc("GET /api/cases/{caseID}/deadlines", deadlineH.ListForCase)
 	scoped.HandleFunc("POST /api/cases/{caseID}/deadlines", deadlineH.Create)
 	scoped.HandleFunc("PUT /api/deadlines/{deadlineID}", deadlineH.Update)
@@ -90,6 +91,7 @@ func New(db *sqlx.DB, authMW *auth.Middleware, cfg *config.Config) http.Handler
 	// Deadline rules (reference data)
 	scoped.HandleFunc("GET /api/deadline-rules", ruleH.List)
 	scoped.HandleFunc("GET /api/deadline-rules/{type}", ruleH.GetRuleTree)
+	scoped.HandleFunc("GET /api/proceeding-types", ruleH.ListProceedingTypes)
 
 	// Deadline calculator
 	scoped.HandleFunc("POST /api/deadlines/calculate", calcH.Calculate)