Add community node protocol spec, Agent Skills, and make the failing tests hermetic

Community nodes (Phase 1 of plan.md): the protocol specification in
services/nodes/spec.py as the single source of truth, GET /nodes/spec.json,
a generated protocol docs page, the Community nodes API docs group, and the
implementation plan plus the residential proxy research. The no-open-proxy rule
is enforced in the spec (open_proxy cannot be set).

Agent Skills: register the Skills API docs group, cascade skills on account
deletion, add the nested CLAUDE.md, README and routes docs, and cover the
parser, the fetcher (end to end against a mock origin), the data layer and the
routes with 73 unit and 16 api tests.

Tests made hermetic with the repo's existing patterns instead of ambient
environment: embeddings tests set OPENROUTER_API_KEY via monkeypatch, the
workspace tests install FakeBackend via runtime.set_backend, and the skills
install tests use run_async. DockerCliBackend now returns 127 (command not
found) when the CLI is missing instead of raising FileNotFoundError, so a host
without docker answers with a clean error rather than a 500. The Providers tab
empty state no longer names the Model routes tab.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

PODMAN.md

@@ -0,0 +1,78 @@
+# Podman deployment (rootless, no docker daemon)
+
+Hosts without a docker daemon (like `devplace`) run the stack with the Python
+`podman-compose` plus the `docker-compose.podman.yml` overlay. The base
+`docker-compose.yml` is unchanged and stays the file rootful `docker compose`
+uses; the overlay only adjusts what rootless podman needs.
+
+## Commands
+
+Always go through the make targets - they pin both `-f` files. A bare
+`podman-compose up -d` drops the overlay and recreates a crashing app (see
+"Why the overlay exists").
+
+```bash
+make podman-build           # build images (only when pyproject/Dockerfiles change)
+make podman-up              # start (also warns if user linger is off)
+make podman-reload          # restart workers on new code (bind-mounted, no rebuild)
+make podman-ps              # container status
+make podman-logs            # tail output
+make podman-down            # stop
+```
+
+Open `http://<host>:${PORT}` (default 10500, published on 127.0.0.1 for the
+front proxy). Source-only changes need just `make podman-reload`.
+
+## Why the overlay exists
+
+The base file runs the app as `user: 1000:1000`, which is correct for rootful
+docker (container uid 1000 == host uid 1000). Under **rootless** podman the
+default userns instead maps container uid 1000 to a subordinate host uid
+(100999), which cannot write the bind-mounted checkout (owned by host uid
+1000) - uvicorn dies on startup with
+`PermissionError: ... '/app/data/locks/devplace-init.lock'`, the app never
+turns healthy, and nginx (which waits on `service_healthy`) never starts.
+
+The overlay sets `user: "0:0"` for the app: container root maps back to the
+invoking host user under rootless, restoring write access while staying
+unprivileged on the host. (`userns_mode: keep-id` would also fix the mapping
+but podman rejects `--userns` together with `--pod`, and podman-compose puts
+all services in one pod.)
+
+## One compose tool only
+
+Use the Python `podman-compose` (`/usr/bin/podman-compose`) for this stack,
+never mix it with native `podman compose` in the same project directory. They
+use different container names (`devplace_app_1` vs `devplace-app-1`) and would
+create a second stack fighting over port 10500.
+
+## Surviving reboots
+
+Both services use `restart: unless-stopped`, but rootless containers only
+restart after a reboot if the host user's systemd linger is enabled:
+
+```bash
+loginctl show-user "$(id -un)" | grep Linger   # want: Linger=yes
+sudo loginctl enable-linger "$(id -un)"        # fix if off
+```
+
+`make podman-up` prints a warning when linger is off.
+
+## Known differences from docker
+
+- The admin-only **Container Manager** needs the docker socket, which does not
+  exist on podman hosts. The `[containers] docker ps failed: [Errno 2]` lines
+  in the app log are expected noise, not an error; serving the site is
+  unaffected.
+- `make docker-attach` / the containers overlay do not apply here.
+
+## Troubleshooting
+
+- `PermissionError ... /app/data/...` on boot: the app was (re)created
+  without the overlay. Run `make podman-up` (it recreates with the fix).
+- `up` hangs with no output: it is waiting on the app healthcheck. In another
+  shell run `podman logs devplace_app_1` - a crash loop there is the cause.
+- `Error: --userns and --pod cannot be set together`: a `userns_mode`
+  override is in play; remove it, this stack relies on `user: "0:0"`.
+- Port 10500 already in use: a second stack (other compose tool, or bare-metal
+  `make prod`) is running. `podman ps -a` plus `ss -tlnp` show the conflict.