Document process-local auth session cache semantics

Clarify that dependencies.py session cache is process-local and not cluster-safe, and document the limitation in architecture docs.

Docs/Architekture.md

@@ -657,6 +657,7 @@ BanGUI maintains its **own SQLite database** (separate from the fail2ban databas
 - The frontend `AuthProvider` checks session validity on mount and redirects to `/login` if invalid.
 - The backend `dependencies.py` provides an `authenticated` dependency that validates the session cookie on every protected endpoint.
 - **Session validation cache** — validated session tokens are cached in memory for 10 seconds (`_session_cache` dict in `dependencies.py`) to avoid a SQLite round-trip on every request from the same browser. The cache is invalidated immediately on logout.
+  This cache is process-local and not safe for multi-worker or distributed deployments. A clustered deployment should replace `_session_cache` with a shared cache or remove it entirely.
 - **Setup-completion flag** — once `is_setup_complete()` returns `True`, the result is stored in `app.state._setup_complete_cached`. The `SetupRedirectMiddleware` skips the DB query on all subsequent requests, removing 1 SQL query per request for the common post-setup case.
 
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