chore(frontend): add the Tavus steering live verification script

[micio86dev]

What

Adds the LIVE Tavus steering verification script used on 2026-10-09 (spike L1 to L8 of tavus-single-session-interview) under scripts/live/, with a README. It SPENDS REAL TAVUS CREDITS and needs the owner's explicit authorization each time; it is never run by tests or CI (rg scripts/live tests is empty).

• tavus-steering-verify.mjs joins ONE existing Tavus conversation as a Daily participant (video off, mic off, headless Chromium with fake devices), exercises the data-channel interactions (steer, leave, observe scenarios) and prints a JSON summary. It never creates or ends a conversation: the caller does that from the api side so the Tavus key never reaches this process. It has no env access and no auth header; the conversation id is printed as its last four characters and the room URL as <redacted>. Output goes under the OS temp directory (--out overrides).
• The 5 lint errors it had are fixed with no behaviour change (merged duplicate imports, an unused constant, a let that is always reassigned, a commented empty catch).
• The README documents prerequisites, the three scenarios with exact command lines, the output, how to create and end the conversation from the api container without printing the key (a browser leave does NOT end it: spike result L7), and the mapping to the live gates G-A to G-D.

Provenance

The original parked file was lost with a scratchpad reset, so this is the version recovered from the transcript of the agent that first wrote it; it may differ from the 2026-10-09 run by later small edits (noted in the README). The api-side helper spike.php was not recoverable and is not included.

Verification

bun run lint 0 errors (3 pre-existing warnings in Input.vue), prettier clean. The script was never run.