feat(rules): project-scoped rules (S3)

Rules can now belong to either a rulebook topic OR a single project,
enforced by a CHECK constraint (exactly-one of topic_id/project_id).
Adds the create_project_rule MCP tool + REST endpoint, surfaces
project-scoped rules in get_project/get_task/start_planning under a
new project_rules field, and adds a project Rules tab section with an
inline create form so the operator can author project rules from the
UI without rulebook ceremony.

- migration 0059: rules.project_id (FK projects ON DELETE CASCADE),
  topic_id now nullable, CHECK ck_rule_topic_xor_project, index on
  project_id
- model: Rule gains project_id; to_dict exposes it
- service: create_project_rule with project-ownership guard; list_rules
  with project_id filter UNIONs subscription-derived + project-scoped;
  get_applicable_rules adds a project_rules field; get_rule / update_rule
  / delete_rule fetch via a shared _fetch_owned_rule that handles both
  rulebook and project ownership paths
- trash: project delete cascades to project-scoped rules
- MCP: create_project_rule tool registered; _INSTRUCTIONS mentions both
  create_rule and create_project_rule paths
- REST: POST /api/projects/<id>/rules (statement required, title derived
  if omitted)
- frontend: Rule type gains nullable topic_id + project_id; createProjectRule
  client; ProjectRulesTab.vue gains a "Project rules" section with inline
  create form and per-rule expand/delete
- tests: register count → 18; create_project_rule unit tests (required
  fields, title derivation, explicit-title pass-through); applicable_rules
  shape tests now include project_rules; trash cascade test updated to
  expect 5 executions

S1+S2 (always_on flag + Scribe-first prompt) shipped in 658348f.
S4 (enter_project handshake) follows.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/test_services_trash.py

@@ -48,18 +48,18 @@ async def test_delete_returns_none_when_not_found():
 
 
 @pytest.mark.asyncio
-async def test_delete_project_cascades_three_tables():
+async def test_delete_project_cascades_to_notes_milestones_and_project_rules():
     session = _make_mock_session()
-    # exists-check + 3 cascade updates (notes, milestones, project)
+    # exists-check + 4 cascade updates (notes, milestones, project-scoped rules, project)
     session.execute = AsyncMock(side_effect=[
-        _exists_result(True), MagicMock(), MagicMock(), MagicMock(),
+        _exists_result(True), MagicMock(), MagicMock(), MagicMock(), MagicMock(),
     ])
     with patch("fabledassistant.services.trash.async_session") as cls:
         cls.return_value = session
         from fabledassistant.services.trash import delete
         batch = await delete(user_id=1, entity_type="project", entity_id=3)
     assert isinstance(batch, str)
-    assert session.execute.await_count == 4
+    assert session.execute.await_count == 5
 
 
 @pytest.mark.asyncio