backend: SSE-Eventstrom /api/events (UMBAU v3 P3a)

- Neuer Router routers/events.py mit EventSource-Endpunkt\n- Heartbeat alle 25s, invalidate-Event bei Status-Änderung\n- Keys: system-status, models, agent-status, ideen, token-stats

backend/app.py

@@ -136,6 +136,7 @@ app.include_router(maintenance.router)
 app.include_router(auftragsbuch.router)   # Vorschlags-Inbox (Mensch-Gate als Klick)
 app.include_router(ideen.router)          # Ideen-Queue (natives Hermes-Kanban) — Tür der Zentrale
 app.include_router(chronik.router)        # Timeline der autonomen Taten (Announce-Store)
+app.include_router(events.router)         # SSE-Eventstrom /api/events (UMBAU v3 P3a)
 app.include_router(eigenleben.router)     # „Von allein": Skills + Vorschlags-Bilanz der Box
 app.include_router(events.router)         # SSE-Eventstrom /api/events (P3a) — Invalidation-Bus
 app.include_router(wissen.router)         # Wissens-Vault (Traum-Notizen) read-only