[idea] Add Tabnine CLI detection

[pucke-dev]

idea / problem

Tabnine CLI (a fork of Gemini CLI) isn't a recognized agent in herdr yet. It runs fine as a plain terminal process, but panes running it get no idle/working/blocked state, sidebar icon, or sound setting — unlike Claude, Codex, Gemini, Cursor, and the other screen-manifest agents.

requested change

Add Tabnine as a new screen-manifest-detected agent.
I have this implemented locally already and can open a PR once this direction is aligned with maintainers.

why you want this

In my enterprise environment, Tabnine CLI is the only coding agent I'm legally permitted to use. Without detection, herdr treats it as a plain terminal — no state tracking, no sidebar signal, no sound cues — so I lose the multi-agent visibility herdr otherwise gives me. Tabnine also shares Gemini CLI's output format, so the detection rules were nearly free to add, bringing it to parity with the other "detected but less tested" agents (Gemini, Cline)

[pucke-dev]

See https://github.com/pucke-dev/herdr/tree/tabnine-detection for my local implementation.