v0.1.22

Update default Gemini model: gemini-2.5-flash -> gemini-3.6-flash

gemini-2.5-flash is no longer available to new API keys (confirmed via a
real "Gemini API request failed" -> now-diagnostic error from the
previous fix, which correctly surfaced Google's actual rejection message
this time instead of a generic one). Updated the default everywhere it
appears: settings.json, the script's fallback, and the Settings tab's
default form value.

Existing installs with a saved (now-stale) model value aren't affected by
this default change - Settings' "Test connection" dropdown already lists
whatever's actually available to a given key, so switching is a Test +
pick-from-dropdown + Save rather than needing a code update.

Bumps to v0.1.22.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>