fix: local management opens without tokens (v2.1.6)

[wicm84266964]

Change

Default loopback management now works without an Admin Token or cookie, so restarting the gateway no longer invalidates open management pages. Local management validates the connection peer, Host, Origin and browser fetch metadata. Explicit token mode remains available and is required for remote listeners; the homepage no longer discloses management credentials.

Startup reserves the port and locks the database before initialization. Repeated launches open the existing instance, and a second process cannot use the same database on another port. The management page opens automatically, with --no-browser available for services. Client API key authentication and CORS behavior are preserved.

Version: 2.1.6, with reviewed release notes.

Validation

• Ran compileall and the full pytest suite, including real subprocess restart, duplicate startup, database locking and management access regression tests.
• Verified the local settings page in Chromium at desktop and mobile widths: no visible Admin Token input and no JavaScript errors.
• Reviewed the changed-file list; no credentials, databases, private account data or runtime output included.
• Will wait for required CI before merging.
• No release tag created or moved in this pull request.