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>

.env.sample

@@ -1,4 +1,29 @@
+# Copy to .env and fill in. Never commit a real key.
+
+# --- DSH Web image (Dockerfile / build.sh) ---
 DEEPSEEK_API_KEY=
 DSH_VERSION=dsh-v0.2.1-rc.2
 PNPM_VERSION=11.28.5
+# DSH Web port inside the container, and the local port published by
+# build.sh / docker run. The gateway also uses it as the upstream port.
 DSH_PORT=3080
+# Comma/space separated extra Host allow-list entries for DSH (for an
+# Ingress/public hostname). localhost and 127.0.0.1 are always trusted.
+DSH_TRUSTED_HOSTS=
+
+# --- Gateway (examples/dsh-agents-as-a-service) ---
+GATEWAY_IMAGE=ghcr.io/sredevopsorg/deepseek-kubernetes-sandbox:gateway
+NAMESPACE=dsh-demo
+POOL=dsh-pool
+# Seconds a sandbox may stay idle before the sweeper suspends it.
+IDLE_TIMEOUT=60
+# Seconds a waking request may wait for the sandbox to become Ready.
+WAKE_TIMEOUT=120
+DSH_CONTAINER=dsh-web
+DSH_LOG_TAIL_LINES=2000
+COOKIE_NAME=dsh_gw_session
+# Set to true only behind HTTPS; secure cookies are not sent over plain HTTP.
+COOKIE_SECURE=false
+COOKIE_MAX_AGE=604800
+MAX_BODY_MB=32
+HTTP_TIMEOUT=300