feat(event-bridge): WP-0003a — domain model, rules module, event type registry

Implements phases 7–8 of the Event Bridge architecture (custodian-WP-0003a).

Domain model (T34, T40):
- Added RuleDef, InstructionDef, ActionDef to models.py
- Updated ActivityDefinition with rules/instructions fields (task_templates deprecated)
- Formalized EventEnvelope: id, type, version, timestamp, publisher, attributes
- Added from_nats_message() and from_webhook_payload() classmethods

Rules module (T35, T36, T37):
- src/activity_core/rules/ skeleton with boundary enforcement
- evaluate_condition() — sandboxed AST walker, whitelisted nodes only, never exec()
- execute_instruction() — LLM task generation with trusted_fields injection guard
- tests/rules/test_boundary.py verifies no cross-boundary imports

Infrastructure (T38, T39):
- Alembic migrations 0004 (task_spawn_log) and 0005 (event_types)
- IssueSink ABC + IssueCoreRestSink (REST) + NullSink (testing)
- TaskSpawnLog and EventType ORM models

Event type registry (T41, T42, T43):
- event_type_registry.py: file scanner, parser, DB sync, in-process lookup
- ACTIVITY_CURATOR_GATE env var (disabled|required) + approve endpoint
- Three org event type definitions: org.repo.registered, org.workstream.completed,
  org.activity.run.completed

All 10 tests pass. Boundary test confirms rules/ isolation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Makefile

@@ -0,0 +1,21 @@
+.PHONY: sync-event-types sync-activity-definitions test
+
+sync-event-types:
+	uv run python -c "
+import asyncio, os
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from activity_core.event_type_registry import sync_event_types
+
+async def main():
+    db_url = os.environ.get('ACTCORE_DB_URL', 'postgresql+asyncpg://actcore:actcore@localhost:5433/actcore')
+    engine = create_async_engine(db_url)
+    factory = async_sessionmaker(engine, expire_on_commit=False)
+    n = await sync_event_types(factory)
+    print(f'Synced {n} event types')
+    await engine.dispose()
+
+asyncio.run(main())
+"
+
+test:
+	uv run pytest tests/ -v