feat(soak): artifacts, graceful shutdown, health probes, smoke script, v3.3.4

Batched remaining harness tasks (27-30, 33):

Task 27 — Artifact capture on failure: screenshots, HTML snapshots,
game state JSON, and console error tails are captured into
tests/soak/artifacts/<run-id>/ when a scenario throws. Successful
runs get a summary.json. Old runs (>7d) are pruned on startup.

Task 28 — Graceful shutdown: first SIGINT/SIGTERM flips the abort
signal (scenarios finish current turn then unwind). 10s after, a
hard-kill fires if cleanup hangs. Double Ctrl-C = immediate exit.
Exit codes: 0 success, 1 errors, 2 interrupted.

Task 29 — Periodic health probes: every 30s GET /health against the
target server. Three consecutive failures abort the run with
health_fatal, preventing staging outages from being misattributed
to harness bugs. Corrected endpoint from /api/health to /health
per server/routers/health.py.

Task 30 — Smoke test script: tests/soak/scripts/smoke.sh, a 60s
end-to-end canary that health-probes the target, seeds if needed,
and runs one minimal populate game.

Task 33 — Version bump to v3.3.4: both index.html footers (was
v3.1.6), new footer added to admin.html (had none), pyproject.toml.

Also fixes discovered during stress testing:
- SessionPool sets baseURL on all contexts so relative goto('/')
  resolves correctly between games (was "invalid URL" error)
- RoomCoordinator key is now unique per game-start (Date.now
  suffix) so Deferred promises don't carry stale room codes from
  previous games

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/soak/core/session-pool.ts

@@ -259,8 +259,13 @@ export class SessionPool {
       // a typical 1920×1080 display. Two windows side-by-side still fit
       // horizontally; if the user runs more than 2 rooms in tiled mode
       // the extra windows will overlap and need to be arranged manually.
+      //
+      // baseURL is set on every context so relative goto('/') calls
+      // (used between games to bounce back to the lobby) resolve to
+      // the target server instead of failing with "invalid URL".
       const context = await targetBrowser.newContext({
         ...this.opts.contextOptions,
+        baseURL: this.opts.targetUrl,
         ...(useHeaded ? { viewport: { width: 960, height: 900 } } : {}),
       });
       await this.injectAuth(context, account);