Make DSH agents-as-a-service browser-usable; fix probe crash-loop (#3)

* Rewrite DSH gateway for browser sessions, HTTP and WebSocket

- Replace the Flask proxy with a Starlette ASGI app (uvicorn factory),
  keeping the control plane (claims, wake/suspend, idle sweeper).
- Add HttpOnly gateway sessions and a server-side DSH launch-token
  handshake: read the token from pod logs, exchange it for a dsh-auth
  cookie, cache per (user, pod UID, Host), refresh once on 401.
- Proxy HTTP/SSE and WebSocket (/api/remote.mux) under /u/<user>/, with
  header stripping/injection, Location rewriting and wake-on-connect.
- Add a landing/signup/login page, health endpoint, pinned dependencies,
  a read-only-rootfs gateway image, 87 cluster-free tests and docs.

* Fix DSH probe crash-loop and harden gateway manifests

- Probe /favicon.svg instead of /: DSH gates / behind its launch-token
  cookie and returns 401, which made warm-pool pods crash-loop.
- Pass DSH_TRUSTED_HOSTS through the entrypoint as --trusted-host args
  for public/ingress hosts; keep localhost trusted.
- Deploy the published :gateway image, add pods/pods-log RBAC, /healthz
  probes, read-only rootfs with a /tmp emptyDir and non-root security.
- Add optional Traefik Ingress and document the prerequisites.

* Update CI, smoke tests, build tooling and docs

- Run gateway pytest/ruff and build/smoke-test the image in CI.
- Parameterize the DSH build version and pnpm version inputs.
- Exercise cookie signup, HTML proxy, WebSocket auth, suspend/wake and
  delete in run-test-kind.sh.
- Add Makefile/build.sh targets and document the architecture, handshake,
  probes, trusted hosts, troubleshooting and limitations.

---------

Co-authored-by: SREDevOpsAgents <agents@sredevops.org>

examples/dsh-agents-as-a-service/gateway/Dockerfile

@@ -1,7 +1,18 @@
 FROM python:3.12-slim
+
+# Read-only-rootfs friendly: no .pyc writes, no home directory writes.
+ENV PYTHONDONTWRITEBYTECODE=1 \
+    PYTHONUNBUFFERED=1 \
+    HOME=/tmp
+
 WORKDIR /app
 COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 COPY gateway.py .
+
+EXPOSE 8080
+# Run as a fixed non-root UID; HOME=/tmp keeps caches out of the image.
 USER 10000
-CMD ["python", "gateway.py"]
+
+CMD ["uvicorn", "gateway:create_app", "--factory", \
+     "--host", "0.0.0.0", "--port", "8080", "--no-access-log"]