Document Stundenplan + Schulkalender end-of-session state

- CLAUDE.md gets a new section summarising the two feature strands,
  pitfalls (Timefold name, JSX quotes, LOC budget), the auth/messaging
  outsourcing, and pointers to the three memory files for next session.
- docs-src/services/schulkalender/ — 5 MkDocs pages mirroring the
  stundenplan structure: index, architecture, holidays, parent-flow,
  notifications. Each with DB tables, endpoints, and the dispatch
  payload contract for the colleague's Matrix/Email services.
- mkdocs.yml gains the Schulkalender nav entry under Services.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mkdocs.yml

@@ -88,6 +88,12 @@ nav:
       - Constraints: services/stundenplan/constraints.md
       - Solver-Tuning: services/stundenplan/solver-tuning.md
       - Export: services/stundenplan/export.md
+    - Schulkalender:
+      - Uebersicht: services/schulkalender/index.md
+      - Architektur: services/schulkalender/architecture.md
+      - Ferien-Snapshot: services/schulkalender/holidays.md
+      - Eltern-Workflow: services/schulkalender/parent-flow.md
+      - Notifications: services/schulkalender/notifications.md
   - Architektur:
     - Multi-Agent System: architecture/multi-agent.md
     - Zeugnis-System: architecture/zeugnis-system.md