desktop: OAuth-aware remote gateway connection

The desktop remote-gateway settings now auto-detect whether a gateway
authenticates with OAuth or a static session token and present the
matching UI + connection mechanism.

Detection: an unauthenticated GET {base}/api/status reads auth_required
(true => OAuth, false => session token); /api/auth/providers supplies the
provider label. The settings UI debounce-probes the entered URL and shows
either a 'Sign in with <provider>' button or the session-token box.

OAuth connection mechanism:
- REST is authed by the HttpOnly session cookie held in a persistent
  Electron session partition (persist:hermes-remote-oauth); main-process
  REST routes through electron net bound to that partition so the cookie
  attaches automatically.
- Login opens a BrowserWindow on {base}/login in that partition and
  resolves once the hermes_session_at cookie lands.
- WebSocket upgrades use a single-use ?ticket= minted at
  POST /api/auth/ws-ticket (the gateway rejects ?token= in gated mode);
  getGatewayWsUrl() re-mints before every (re)connect since tickets are
  single-use and short-lived.
- Missing cookie / 401 surfaces needsOauthLogin to prompt re-sign-in
  (Nous Portal contract v1 issues no refresh token).

Local and token modes are unchanged.

Pure helpers (URL normalize, ws-url token/ticket builders, auth-mode
classify/resolve, cookie detector) are extracted to a standalone
connection-config.cjs (no electron import) and unit-tested with
node --test (26 tests), matching the backend-probes.cjs pattern.

apps/desktop/package.json

@@ -35,7 +35,7 @@
     "test:desktop:nsis": "node scripts/test-desktop.mjs nsis",
     "test:desktop:existing": "node scripts/test-desktop.mjs existing",
     "test:desktop:fresh": "node scripts/test-desktop.mjs fresh",
-    "test:desktop:platforms": "node --test electron/bootstrap-platform.test.cjs electron/hardening.test.cjs electron/backend-probes.test.cjs electron/bootstrap-runner.test.cjs",
+    "test:desktop:platforms": "node --test electron/bootstrap-platform.test.cjs electron/hardening.test.cjs electron/backend-probes.test.cjs electron/bootstrap-runner.test.cjs electron/connection-config.test.cjs",
     "type-check": "tsc -b",
     "lint": "eslint src/ electron/",
     "lint:fix": "eslint src/ electron/ --fix",