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>

devplacepy/database/schema.py

@@ -1849,6 +1849,7 @@ def init_db():
     )
 
     _ensure_moderation_tables()
+    _ensure_skills_table()
 
     for table in db.tables:
         _uid_index(db, table)
@@ -2151,6 +2152,45 @@ MODERATION_INDEXES: tuple[tuple[str, str, list[str]], ...] = (
 )
 
 
+SKILLS_COLUMNS: tuple[tuple[str, object], ...] = (
+    ("uid", ""),
+    ("user_uid", ""),
+    ("name", ""),
+    ("description", ""),
+    ("body", ""),
+    ("files", ""),
+    ("source_url", ""),
+    ("license", ""),
+    ("compatibility", ""),
+    ("metadata", ""),
+    ("allowed_tools", ""),
+    ("enabled", 1),
+    ("sha256", ""),
+    ("skipped", ""),
+    ("warnings", ""),
+    ("fetched_at", ""),
+    ("created_at", ""),
+    ("updated_at", ""),
+    ("deleted_at", ""),
+    ("deleted_by", ""),
+)
+
+
+def _ensure_skills_table() -> None:
+    table = get_table("skills")
+    for column, example in SKILLS_COLUMNS:
+        if not table.has_column(column):
+            table.create_column_by_example(column, example)
+    _index(db, "skills", "idx_skills_user_name", ["user_uid", "name"], unique=True)
+    _index(
+        db,
+        "skills",
+        "idx_skills_user_live",
+        ["user_uid", "enabled"],
+        where="deleted_at IS NULL",
+    )
+
+
 def _ensure_moderation_tables() -> None:
     for table_name, columns in MODERATION_COLUMNS.items():
         table = get_table(table_name)