Let the candidate control when agent takes the turn

[jserv]

Jim answered the pause a candidate took to find the next word, and kept talking after a candidate asked for time to think. The first commit raises the default silence window from one second to three, tells the interviewer a pause within a sentence is not a finished answer, and adds "Your turn is done" (a button, Alt+Enter, or a click on a countdown ring that fills through the window while the microphone is quiet), which ends the audio stream so Gemini answers without waiting it out. The second adds a thinking hold: a Thinking button or an explicit spoken request in English ("let me think", "can you give me a minute") keeps the floor, generated replies are dropped, nudges wait, hints and endings are refused, and evidence and the deadline carry on. Speaking again, Continue or yielding ends it, and so do the five-minute warning, the round change and one check-in after two silent minutes.

The trade worth a reviewer's eye is the longer window: three seconds would slow every reply, which is why the yield exists, and it only helps if ending the audio stream really ends the turn. A probe against the live API (9 sessions, gemini-3.1-flash-live-preview, 3s window) measured the first reply audio at a median 0.76s after the last word with audioStreamEnd against 3.36s without; the next utterance after it was detected normally, and 1 turn in 12 ignored the end and fell back to the full window. The same probe showed inputTranscription.finished is never sent and the transcript arrives about 0.3s after the stream ends, which is what the pre-click transcript window in the hold is sized from. Spoken requests are matched by phrase, so recognition is English only and deliberately strict: short phrases such as "one second" or "hold on" count only as a whole sentence.

Verified with scripts/test.sh at each commit (all gates pass; at the tip 1061 Rust tests and 647 browser tests, with the Playwright lane skipped because Chromium is unsupported on this Ubuntu 20.04 host). Before the rebase onto current main: with Chromium 130 linked in by hand the browser suite passed 753 of 757, the 4 failures being PDF tests that fail identically on main, and credentialed scripts/browser-check.sh with the rust agent passed the voice, barge and report flows, and a scripted run against a real room clicked Thinking, saw Jim stay listening for the whole hold, released it by speaking and by Continue, and yielded with Alt+Enter. scripts/gemini-check.sh gets setupComplete with the new window. cargo mutants --in-diff over the change found 10 missed and 4 timeouts; after new tests, and with the three functions that only write to the room added to the exclusion list with the reason, a re-run over the affected functions caught all 63 viable mutants. It was not re-run after the final cleanup. The prompt golden changes on purpose: contract bundle 22, live prompt 14.

Closes #140
Closes #172

---

Summary by cubic

Lets candidates control when Jim takes or gives up the turn. The default silence window increases from one to three seconds so a pause mid-sentence is not treated as a finished answer, while Your turn is done (a button, Alt+Enter, or the countdown ring) ends the audio turn immediately.

• Adds a Thinking hold started by the Thinking button or an explicit spoken request in English; replies generated during a hold are dropped and hints, nudges, and endings wait.
• Ends the hold when the candidate speaks, chooses Continue, yields the turn, or after the five-minute warning, the round transition, or a single check-in after two silent minutes.
• Keeps the editor, microphone, evidence, and deadline active throughout, and records thinking lifecycle events in evidence and replay views.
• Covers review gaps: failed cold briefings no longer drop their reply, spoken holds no longer inherit the button's release cooldown, the turn ring stops when the mic fails or no interviewer is present, and system events can end a hold.
• Bumps the contract bundle to 25 with live prompt 17. Closes Jim often cuts in before I finish speaking #140 and Interviewer keeps talking even I asks for time to think #172.

^{Written for commit 271e939. Summary will update on new commits.}