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.

frontend/src/app/(app)/fristen/rechner/page.tsx

@@ -1,28 +1,61 @@
 "use client";
 
 import { DeadlineCalculator } from "@/components/deadlines/DeadlineCalculator";
+import { DeadlineWizard } from "@/components/deadlines/DeadlineWizard";
 import { ArrowLeft } from "lucide-react";
 import Link from "next/link";
+import { useState } from "react";
 
 export default function FristenrechnerPage() {
+  const [mode, setMode] = useState<"wizard" | "quick">("wizard");
+
   return (
     <div className="animate-fade-in space-y-4">
-      <div>
-        <Link
-          href="/fristen"
-          className="mb-2 inline-flex items-center gap-1 text-sm text-neutral-500 transition-colors hover:text-neutral-700"
-        >
-          <ArrowLeft className="h-3.5 w-3.5" />
-          Zurück zu Fristen
-        </Link>
-        <h1 className="text-lg font-semibold text-neutral-900">
-          Fristenrechner
-        </h1>
-        <p className="mt-0.5 text-sm text-neutral-500">
-          Berechnen Sie Fristen basierend auf Verfahrensart und Auslösedatum
-        </p>
+      <div className="flex items-start justify-between">
+        <div>
+          <Link
+            href="/fristen"
+            className="mb-2 inline-flex items-center gap-1 text-sm text-neutral-500 transition-colors hover:text-neutral-700"
+          >
+            <ArrowLeft className="h-3.5 w-3.5" />
+            Zurueck zu Fristen
+          </Link>
+          <h1 className="text-lg font-semibold text-neutral-900">
+            Fristenbestimmung
+          </h1>
+          <p className="mt-0.5 text-sm text-neutral-500">
+            {mode === "wizard"
+              ? "Vollstaendige Verfahrens-Timeline mit automatischer Fristenberechnung"
+              : "Schnellberechnung einzelner Fristen nach Verfahrensart"}
+          </p>
+        </div>
+
+        {/* Mode toggle */}
+        <div className="flex rounded-md border border-neutral-200 bg-neutral-50 p-0.5">
+          <button
+            onClick={() => setMode("wizard")}
+            className={`rounded px-3 py-1 text-xs font-medium transition-colors ${
+              mode === "wizard"
+                ? "bg-white text-neutral-900 shadow-sm"
+                : "text-neutral-500 hover:text-neutral-700"
+            }`}
+          >
+            Verfahren
+          </button>
+          <button
+            onClick={() => setMode("quick")}
+            className={`rounded px-3 py-1 text-xs font-medium transition-colors ${
+              mode === "quick"
+                ? "bg-white text-neutral-900 shadow-sm"
+                : "text-neutral-500 hover:text-neutral-700"
+            }`}
+          >
+            Schnell
+          </button>
+        </div>
       </div>
-      <DeadlineCalculator />
+
+      {mode === "wizard" ? <DeadlineWizard /> : <DeadlineCalculator />}
     </div>
   );
 }