add OAuth defaults and admin reservation deletion support

Seed rms.auth.oauth plugin settings with a Google OIDC example while keeping the plugin disabled by default, add admin API/UI support to delete individual reservation entries, and extend auth flow handling for OAuth callback redirects and errors.

README.md

@@ -38,6 +38,16 @@ Auth
 - `rms.auth.otp_email`: OTP challenge delivery through email
 - `rms.auth.oauth`: OAuth/OIDC authorization-code login (disabled by default; configurable authorize/token/userinfo/client settings)
 
+Google example (plugin settings):
+- `authorizeUrl`: `https://accounts.google.com/o/oauth2/v2/auth`
+- `tokenUrl`: `https://oauth2.googleapis.com/token`
+- `userInfoUrl`: `https://openidconnect.googleapis.com/v1/userinfo`
+- `scope`: `openid email profile`
+- `emailField`: `email`
+- `clientId`: `<google-client-id>.apps.googleusercontent.com`
+- `clientSecret`: `<google-client-secret>`
+- `redirectUri`: `<public-base-url>/v1/auth/oauth/callback` (or leave empty to auto-derive)
+
 Station & Access
 - `rms.station.shell`: station activation/deactivation command execution
 - `rms.station.access.policy`: export effective access list for OpenWebRX policies