[idea] Antigravity CLI integration support

[ludoo]

idea / problem

Add antigravity-cli (agy) as a first class citizine in herdr. Antigravity-cli is the successor to gemini-cli, and the native cli harness for Gemini.

requested change

Antigravity-cli with feature parity to the other supported harnesses.

why you want this

Because I have a Gemini subscription, and use agy as my harness when I work with Gemini.

Provisional support added here ludoo#1

[ludoo]

Any chance I can open a PR with this? I have it working locally, and it's pretty useful to anyone with a Gemini sub.

[bradshimmin]

Sounds great here. I'd appreciate integration support for Gemini CLI itself, if possible, folks.

[LiQuBit]

agy is Herdr's internal canonical agent kind identifier (alongside claude, codex, pi, etc.). It uses this identifier in its screen-scraper, process inspector, and session hooks (~/.gemini/config/hooks/herdr-agent-state.sh) to detect Antigravity's lifecycle states (idle, working, blocked, done). But, quite often, when installing Antigravity, a user like me may choose to use a different name for launching different flavors of Antigravity agent, say, agycli for Antigravity CLI, agy for the Antigravity App (UI), and agyide for the Antigravity IDE. Hence, it will be good to allow users to configure Herdr for detecting Antigravity agent using the process name of their choice. This feature should be generalized to support other agents as well.