fix(gemini): read Gemini CLI's composer bar and spinner line so a turn can end

A gemini session stayed "working" for good after its first turn. Its braille
spinner trips the generic SPINNER_PATTERN and marks the pane working, but only
a composer glyph arms the idle confirmation and gemini declared none, so it
fell back to Claude's `❯`, which gemini never draws.

Measured on live Gemini CLI 0.63.0 panes (capture-pane every 300 ms through
real turns with a shell call at 40, 120 and 200 columns, YOLO and default
approval mode, plus the raw PTY stream). The turns ran against a local
stand-in for the Gemini API (GOOGLE_GEMINI_BASE_URL, which Codeman's custom
endpoint support already sets), since the CLI's TUI does not depend on the
backend and no account is needed for it:

- The TUI repaints its whole bottom region every frame, composer included,
  and the composer sits between a `▄` bar and a `▀` bar; the submitted prompt
  is echoed between the same bars. The `▀` bar arms the idle check: every
  repaint carries it, tmux's reattach repaint too. The composer's prompt
  character is no good: it follows the approval mode (`*` in YOLO), and its
  `>` also starts the echoed prompt, which would make the submit verifier
  read a submitted prompt as stranded and press Enter again.
- While a turn runs a line `⠦ Thinking... (esc to cancel, 6s)` animates about
  every 80 ms (largest gap mid-turn: 214 ms). The label can be any loading
  phrase, so the working line is the `(esc to cancel, <n>` suffix, or a
  spinner frame opening a line for when a long phrase wraps that suffix.
  Nothing at rest matches either.
- A tool confirmation (default mode) replaces the composer, stops the
  spinner and the pane goes silent (3.9 s gap), so it reads as idle.

Verified on an isolated instance from this branch: a YOLO turn emitted one
session:working (+170 ms) and one session:idle (2.5 s after the last output);
a default-mode turn went working -> idle while the confirmation waited ->
working once allowed -> idle at the end; after a server restart four restored
gemini panes went busy -> idle in about 4 s; a fresh launch settled in 3 s.

The launch-settle and uncharacterised-CLI tests that used gemini as their
example of a CLI without work detection now use grok and deepseek.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/session.ts

@@ -4485,7 +4485,7 @@ export class Session extends EventEmitter {
           : this._mux.capturePaneText?.(this._muxSession.muxName),
       sendEnter: () => this._mux?.sendInput(this.id, '\r'),
       // ⚠ NO fallback glyph here, unlike the screen-reading probe elsewhere in this file.
-      // Only claude, codex, pi, opencode and omp declare a promptGlyph; the other modes would fall back
+      // Only claude, codex, pi, opencode, omp and gemini declare a promptGlyph; the other modes would fall back
       // to claude's `❯`, which is ALSO starship's default shell prompt (and pure's, and
       // spaceship's, and p10k lean's). On a shell session the line `❯ npm run build` sits
       // on screen for as long as the command runs, promptStillInComposer() reads that as