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>

Dockerfile

@@ -76,6 +76,7 @@ set -eu
 
 : "${DSH_PORT:=3080}"
 : "${DSH_HOST:=}"
+: "${DSH_TRUSTED_HOSTS:=}"
 DSH_PUBLIC_URL="${DSH_PUBLIC_URL-http://localhost:${DSH_PORT}}"
 
 # DSH rejects wildcard hosts. Pick the container/pod's first non-loopback IPv4.
@@ -87,6 +88,18 @@ if [ -n "$DSH_PUBLIC_URL" ]; then
   set -- --public-url "$DSH_PUBLIC_URL" "$@"
 fi
 
+# Additional trusted hosts (e.g. the public gateway host behind an Ingress).
+# DSH Host/Origin-fences /api: without this, requests forwarded with the
+# browser's Host header are rejected. Accepts comma- or space-separated names;
+# localhost/127.0.0.1 are always trusted below.
+old_ifs="$IFS"
+IFS=', '
+for trusted_host in $DSH_TRUSTED_HOSTS; do
+  [ -n "$trusted_host" ] || continue
+  set -- "$@" --trusted-host "$trusted_host"
+done
+IFS="$old_ifs"
+
 exec node /app/lib/bin.js web \
   --no-open \
   --host "$DSH_HOST" \