Add SaveToken, LoadToken, and DeleteToken hook fields to edition.Hooks so overlay builds can provide custom token storage. Refactor SaveTokenData, LoadTokenData, and DeleteTokenData to delegate to hooks when present, falling back to default keychain-based storage.
- Add AuthClientID and AuthClientFromMCP fields to edition Hooks, allowing overlays to override the default OAuth client ID and route auth through MCP endpoints.
- Introduce token marker file (token.json) mechanism so the host application in embedded mode can detect authentication state without accessing the keychain.
- Update SaveTokenData/DeleteTokenData to write/remove the marker file when running in embedded mode.
- Update ClientID() and IsClientIDFromMCP() to respect edition overrides.
When logging in with --client-id and --client-secret, credentials are now
automatically persisted to enable automatic token refresh after expiration.
Client secret is securely stored in system Keychain, config file only
contains a reference.
wxianfeng