feat(sprint8): Phase 3 — Mitgliederversammlung (assemblies, voting, protocol PDF)

Backend:
- V19 migration: assemblies, assembly_agenda_items, assembly_attendees, assembly_votes, assembly_vote_records
- Enums: AssemblyType, AssemblyStatus, AgendaItemType, VoteType, VoteDecision, VoteResult
- Entities: Assembly, AssemblyAgendaItem, AssemblyAttendee, AssemblyVote, AssemblyVoteRecord
- Repositories: Assembly, AgendaItem, Attendee, Vote, VoteRecord
- AssemblyService: full lifecycle (create, invite, start, attend, vote, quorum, complete)
- AssemblyProtocolService: OpenPDF protocol generation (§147 AO compliant)
- AssemblyController: admin + portal endpoints
- Extended: AuditEventType, NotificationType, StaffPermission

Frontend:
- Assembly service with full API client and TypeScript types
- Admin assemblies list page with create dialog (agenda builder)
- Admin assembly detail page (quorum, agenda, votes, attendees)
- Navigation: Versammlungen with Gavel icon (after Finanzen)

Legal basis: §32-§40 BGB (Mitgliederversammlung), §147 AO (retention)

cannamanage-frontend/src/data/navigations.ts

@@ -44,6 +44,11 @@ export const navigationsData: NavigationType[] = [
         href: "/finance",
         iconName: "Wallet",
       },
+      {
+        title: "Versammlungen",
+        href: "/assemblies",
+        iconName: "Gavel",
+      },
       {
         title: "Kalender",
         href: "/calendar",