Phase 0, Task 0.3. start_server now computes should_require_auth(host,
allow_public) and records it on app.state.auth_required BEFORE the
existing legacy SystemExit guard fires. This gives middleware, the SPA
token-injection path, and WS endpoints a consistent read source for
'is the gate active'. The flag is set but no one reads it yet — Phase 3
registers the gate middleware.
Note: 4 pre-existing test failures in tests/hermes_cli/test_web_server.py
(PtyWebSocket) + test_update_hangup_protection.py reproduce on pristine
HEAD and are unrelated to this change (starlette TestClient WS regression).
Phase 0, Task 0.2. Single source of truth for 'is the auth gate active?'.
Reuses the existing _LOOPBACK_HOST_VALUES frozenset so this stays in sync
with the DNS-rebinding host-header check. RFC1918/CGNAT/link-local are
treated as public — exact threat model the gate exists for.
Phase 0, Task 0.1 of the dashboard-oauth plan. Establishes a baseline for
the loopback dashboard's auth surface so future phases can prove they
didn't regress the existing _SESSION_TOKEN flow when adding the OAuth gate.
