Prove video flows: an e2e suite with a real WebRTC viewer

e2e-edge.sh proves the camera signalling relay round-trips, and says so
honestly - it posts a stub SDP with go2rtc absent and accepts a 503 that
came back from the gateway. But "the offer round-trips" says nothing
about whether anyone would see a picture, and it once read as more than
it was: a stray go2rtc left over from an earlier run answered the stub
with an HTTP 500 and the test still printed ok. Video had never been
shown to flow.

scripts/e2e-camera.sh runs the real backend, the real proxy and the real
go2rtc against the H2C, and scripts/e2e-camera-peer.ts plays the
browser's part with werift: createOffer, relay through the backend,
setRemoteDescription, then ICE, DTLS and SRTP, counting RTP out the far
end. Measured: 124-149 packets and ~119-147 KB of payload within a
second or two. It sends no printer command; the camera is a pull and the
MQTT subscription is passive. It refuses to start if a go2rtc is already
running, and fails if one survives cleanup.

werift is a devDependency for that one file; nothing under src/ imports
it. Its 30 resolved packages were audited against LICENSES.md: 26 MIT,
Apache-2.0, BSD-3-Clause, Unlicense, and one MPL-2.0 (mediabunny), which
the policy allows while we do not edit its files.

Smaller fixes in the same pass:

- e2e-edge.sh now unsets the TURN variables. It asserts TURN is off, but
  sourcing dev-secrets.sh turns it on, and the failure message then
  printed the live Cloudflare username and credential. The new script
  prints only the camera id and a count, never the /stream body.
- the last hardcoded `psql -h localhost` in e2e-edge.sh now uses
  DATABASE_URL, like the rest.

package.json

@@ -29,8 +29,9 @@
     "ioredis": "^5.4.1"
   },
   "devDependencies": {
-    "drizzle-kit": "0.24.2",
     "bun-types": "^1.1.10",
-    "typescript": "^5.6.2"
+    "drizzle-kit": "0.24.2",
+    "typescript": "^5.6.2",
+    "werift": "^0.25.1"
   }
 }