feat: UPC deadline determination — event-driven model with proceeding timeline

Full event-driven deadline determination system ported from youpc.org:

Backend:
- DetermineService: walks proceeding event tree, calculates cascading
  dates with holiday adjustment and conditional logic
- GET /api/proceeding-types/{code}/timeline — full event tree structure
- POST /api/deadlines/determine — calculate timeline with conditions
- POST /api/cases/{caseID}/deadlines/batch — batch-create deadlines
- DeadlineRule model: added is_spawn, spawn_label fields
- GetFullTimeline: recursive CTE following cross-type spawn branches
- Conditional deadlines: condition_rule_id toggles alt_duration/rule_code
  (e.g. Reply changes from RoP.029b to RoP.029a when CCR is filed)
- Seed SQL with full UPC event trees (INF, REV, CCR, APM, APP, AMD)

Frontend:
- DeadlineWizard: interactive proceeding timeline with step-by-step flow
  1. Select proceeding type (visual cards)
  2. Enter trigger event date
  3. Toggle conditional branches (CCR, Appeal, Amend)
  4. See full calculated timeline with color-coded urgency
  5. Batch-create all deadlines on a selected case
- Visual timeline tree with party icons, rule codes, duration badges
- Kept existing DeadlineCalculator as "Schnell" quick mode

Also resolved merge conflicts across 6 files (auth, router, handlers)
merging role-based permissions + audit trail features.

backend/internal/auth/context.go

@@ -9,19 +9,11 @@ import (
 type contextKey string
 
 const (
-<<<<<<< HEAD
 	userIDKey    contextKey = "user_id"
 	tenantIDKey  contextKey = "tenant_id"
 	ipKey        contextKey = "ip_address"
 	userAgentKey contextKey = "user_agent"
-||||||| 82878df
-	userIDKey   contextKey = "user_id"
-	tenantIDKey contextKey = "tenant_id"
-=======
-	userIDKey   contextKey = "user_id"
-	tenantIDKey contextKey = "tenant_id"
-	userRoleKey contextKey = "user_role"
->>>>>>> mai/pike/p0-role-based
+	userRoleKey  contextKey = "user_role"
 )
 
 func ContextWithUserID(ctx context.Context, userID uuid.UUID) context.Context {
@@ -41,7 +33,6 @@ func TenantFromContext(ctx context.Context) (uuid.UUID, bool) {
 	id, ok := ctx.Value(tenantIDKey).(uuid.UUID)
 	return id, ok
 }
-<<<<<<< HEAD
 
 func ContextWithRequestInfo(ctx context.Context, ip, userAgent string) context.Context {
 	ctx = context.WithValue(ctx, ipKey, ip)
@@ -62,8 +53,6 @@ func UserAgentFromContext(ctx context.Context) *string {
 	}
 	return nil
 }
-||||||| 82878df
-=======
 
 func ContextWithUserRole(ctx context.Context, role string) context.Context {
 	return context.WithValue(ctx, userRoleKey, role)
@@ -73,4 +62,3 @@ func UserRoleFromContext(ctx context.Context) string {
 	role, _ := ctx.Value(userRoleKey).(string)
 	return role
 }
->>>>>>> mai/pike/p0-role-based