feat: vollständiges Datenmodell für Normen und Entscheidungen (AIIA-15)

Replaces placeholder schema with full legal data model:
- Normen with temporal versioning (valid_from/valid_to), source rank hierarchy,
  immutable version chains, and norm-to-norm cross-references
- Entscheidungen with structured metadata (Aktenzeichen, Gremium, Leitsatz,
  Tenor, Tatbestand, Entscheidungsgründe), decision-norm links with Stichtag
- NV Bühne Fachgruppen and BSchGO Arbitration Tribunals
- Cases, Analyses, and DSGVO Audit Log
- Mandantentrennung via tenant_id + PostgreSQL Row-Level Security policies
- Initial Drizzle migration and RLS migration

Co-Authored-By: Paperclip <noreply@paperclip.ing>

drizzle/meta/_journal.json

@@ -0,0 +1,13 @@
+{
+  "version": "7",
+  "dialect": "postgresql",
+  "entries": [
+    {
+      "idx": 0,
+      "version": "7",
+      "when": 1775682934077,
+      "tag": "0000_peaceful_amazoness",
+      "breakpoints": true
+    }
+  ]
+}