feat(trainer): training from the collector UI — the trainer becomes a job service, the review page gains a Training section

Trainer: `parking-trainer serve` — a stdlib HTTP job API on the compose network (never
published): /health, /readiness, /versions, /versions/<v>/report, /jobs. One job at a
time; each job runs the CLI as a subprocess with its output captured, state + log
persisted under /out/jobs/ so a restart keeps history. `publish` takes its URL from
TRAINER_PUBLISH_URL. Dockerfile: CMD serve, EXPOSE 8091, healthcheck.

Collector: COLLECTOR_TRAINER_URL + /api/training/{status,jobs,jobs/:id,versions/:v/report}
— a reviewer-gated proxy that forwards a fixed set of paths and whitelisted knobs and
passes the trainer's status codes through (409 while a job runs; 503 unconfigured, 502
unreachable). /review gains the Training section: labels per class vs the minimum with
Train disabled until two classes clear it, mode / backbone / floor, the running job's
live log, the versions with Report / Evaluate / Publish (publish confirms), and the
reminder that pinning stays a git commit. Fixed on the way: an apostrophe in the page's
inline script broke the whole page — a test now parses the script.

Compose: `trainer` is a service (restart: unless-stopped, read-only data volume, its own
trainer-out volume), the `train` profile and TRAINER_OUT are gone; the Docker-socket
route was rejected (root on the host for a service booths upload to). Verified with both
images running together: a Train started through the proxy finished, version and report
came back, the page rendered.

Wiki: bodytype-classifier-training (loop, running it, operating notes superseded),
vision-review-outbox, fleet-deployment-komodo, log.

Claude-Session: https://claude.ai/code/session_01FWncR69HgGPuei1dLrW3cU

apps/trainer/README.md

@@ -25,12 +25,12 @@ A passing run writes `<out>/<version>/`:
 | `report.md` | the human report: accuracy, per-class recall/precision, confusion matrix, dropped classes, loss weights |
 | `metrics.json` | the same numbers, machine-readable |
 
-On the reviewer's host (the `wash-collector` stack):
-
-```
-docker compose -f docker-compose.collector.yml --profile train run --rm trainer inspect
-docker compose -f docker-compose.collector.yml --profile train run --rm trainer train --min-accuracy 0.85
-```
+On the reviewer's host the image runs `serve` as the `trainer` service of the
+`wash-collector` stack: a job API (`/health`, `/readiness`, `/versions`, `/jobs`) on the compose
+network that the collector's **Training section** (`/review`) drives — readiness, Train /
+Evaluate / Publish, reports and logs. Jobs run as subprocesses of the CLI, one at a time; state
+and logs persist under `/out/jobs/`. The CLI stays for debugging:
+`docker compose -f docker-compose.collector.yml exec trainer parking-trainer inspect`.
 
 Local dev: `uv sync --extra train` (CPU torch, ~200 MB), `uv run pytest -q`. The test suite
 runs without the extra (torch tests skip), matching CI.