feat: add OpenAI OAuth, strict model overrides, and Gmail pull mode

src/frontends/tui/commands.ts

@@ -124,7 +124,7 @@ Commands:
   /model [name]          Show or switch model tier (local, default, fast, complex)
   /model <tier> <p/m>    Change tier's provider/model (e.g. /model default anthropic/claude-sonnet-4)
   /backend [provider]    Show or switch local backend (ollama, llamacpp)
-  /login [provider]      Authenticate with GitHub
+  /login [provider]      Authenticate with GitHub or OpenAI
   /pair                  List pending pairing codes and approved senders
   /pair generate [label] Generate a new DM pairing code
   /pair revoke <ch> <id> Revoke an approved sender
@@ -178,7 +178,7 @@ export const COMMAND_TOOLTIPS: Record<string, string> = {
   '/status': 'Show session info and token usage',
   '/fullscreen': 'Switch to fullscreen mode',
   '/fs': 'Switch to fullscreen mode',
-  '/login': 'Authenticate with GitHub (OAuth device flow)',
+  '/login': 'Authenticate with GitHub or OpenAI (OAuth device flow)',
   '/pair': 'Generate/list/revoke DM pairing codes',
   '/transfer': 'Transfer session to another frontend',
   '/quit': 'Exit TUI',