fix(contract-drift): MCP read-only scope, shared-note writes, event TZ

Drift-audit Group 5 (high-severity contract drift):

- MCP read-only keys could call every write tool: the Bearer resolver
  discarded api_key.scope and dispatch had no gate. Add resolve_bearer()
  (returns user_id + scope) and a scope gate in the /mcp ASGI wrapper that
  buffers the JSON-RPC body and rejects tools/call for any tool outside a
  read all-list when scope=='read' (default-deny for unknown/new tools).
- Shared project notes/tasks panel was empty for non-owners: get_project_notes_route
  now queries notes/milestones with the project OWNER's uid (mirrors the
  already-fixed milestones route).
- Shared editors couldn't save/delete shared NOTES (tasks worked): the three
  notes write routes now resolve via get_note_for_user, gate on can_write_note,
  and write as the owner — matching the tasks routes.
- Event timezone drift: naive datetimes from the MCP date+time split are now
  localized to the user's tz at a single canonical service point (create_event
  /update_event), so MCP- and UI-created events agree. tz-aware inputs
  (REST/CalDAV) pass through untouched.
- create_note validates status/priority (TaskStatus/TaskPriority), closing the
  MCP create_task path that let out-of-enum values persist (no DB CHECK).

Tests cover resolve_bearer scope + the write-tool classifier.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_mcp_auth.py

@@ -49,3 +49,47 @@ async def test_resolve_bearer_calls_lookup_with_stripped_token():
     with patch("fabledassistant.mcp.auth.lookup_key", mock_lookup):
         await resolve_bearer_to_user_id("Bearer fmcp_abc123  ")
     mock_lookup.assert_awaited_once_with("fmcp_abc123")
+
+
+# ── resolve_bearer (user_id + scope) ────────────────────────────────────
+
+@pytest.mark.asyncio
+async def test_resolve_bearer_returns_user_id_and_scope():
+    from fabledassistant.mcp.auth import resolve_bearer
+    fake_key = MagicMock()
+    fake_key.user_id = 9
+    fake_key.scope = "read"
+    with patch("fabledassistant.mcp.auth.lookup_key", AsyncMock(return_value=fake_key)):
+        assert await resolve_bearer("Bearer fmcp_x") == (9, "read")
+
+
+@pytest.mark.asyncio
+async def test_resolve_bearer_none_for_invalid():
+    with patch("fabledassistant.mcp.auth.lookup_key", AsyncMock(return_value=None)):
+        assert await resolve_bearer("Bearer nope") is None
+    assert await resolve_bearer(None) is None
+
+
+# ── read-only scope gate ────────────────────────────────────────────────
+
+def test_body_calls_write_tool_classifies_correctly():
+    import json
+    from fabledassistant.mcp.server import _body_calls_write_tool
+
+    def call(name):
+        return json.dumps({"jsonrpc": "2.0", "id": 1, "method": "tools/call",
+                           "params": {"name": name, "arguments": {}}}).encode()
+
+    # Write-class tools are gated.
+    assert _body_calls_write_tool(call("create_note")) is True
+    assert _body_calls_write_tool(call("delete_project")) is True
+    assert _body_calls_write_tool(call("purge_trash")) is True
+    # An unknown/new tool defaults to write (default-deny for read keys).
+    assert _body_calls_write_tool(call("brand_new_tool")) is True
+    # Read tools and non-call methods pass.
+    assert _body_calls_write_tool(call("list_notes")) is False
+    assert _body_calls_write_tool(call("get_recent")) is False
+    assert _body_calls_write_tool(
+        json.dumps({"method": "tools/list"}).encode()
+    ) is False
+    assert _body_calls_write_tool(b"not json") is False