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>

tests/api/projects/workspace.py

@@ -7,7 +7,8 @@ import pytest
 
 from devplacepy.content import can_manage_workspace, can_open_workspace
 from devplacepy.database import get_table, init_db, set_setting
-from devplacepy.services.containers import activity, api, store
+from devplacepy.services.containers import activity, api, runtime, store
+from devplacepy.services.containers.backend.fake import FakeBackend
 from devplacepy.services.containers.workspace import (
     editor,
     flags,
@@ -29,7 +30,9 @@ HTTP_TIMEOUT = 30
 def _workspace_db():
     init_db()
     set_setting("workspace_enabled", "1")
+    runtime.set_backend(FakeBackend())
     yield
+    runtime.set_backend(None)
     for table in (
         "instances",
         "tunnels",