feat(spaces): implement Phase 2 Event System

Week 4 - Event Infrastructure:
- Create SpaceEventType enum with 18 event types covering space lifecycle,
  document operations, variables, references, rendering, sync, and cache
- Create SpaceEvent dataclass with serialization/deserialization
- Create EventBus with sync/async handler support, priority ordering,
  global handlers, and optional event history
- Add event factory functions for common events

Week 5 - Event Integration:
- Wire EventBus into SpaceService as optional dependency
- Emit events for all space operations:
  - SPACE_CREATED, SPACE_UPDATED, SPACE_DELETED, SPACE_ACTIVATED, SPACE_ARCHIVED
  - DOCUMENT_ADDED, DOCUMENT_REMOVED, DOCUMENT_MOVED, DOCUMENT_CONTENT_CHANGED
  - VARIABLE_SET, VARIABLE_DELETED
- Create integration tests for event propagation patterns

Test coverage: 187 tests total
- 43 unit tests for event system
- 20 integration tests for event propagation
- 124 existing tests continue to pass

Capabilities delivered:
- CAP-010: SpaceEvent base with type, payload, timestamp
- CAP-011: EventBus with in-process publish/subscribe
- CAP-012: Event handlers registry with priority support
- CAP-013: Change detection via content hash comparison

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

markitect/spaces/__init__.py

@@ -51,6 +51,15 @@ from .repositories import (
     initialize_space_tables,
 )
 
+# Phase 2: Event System
+from .events import (
+    SpaceEvent,
+    SpaceEventType,
+    EventBus,
+    get_event_bus,
+    reset_event_bus,
+)
+
 __all__ = [
     # Models
     "InformationSpace",
@@ -73,4 +82,10 @@ __all__ = [
     "SqliteVariableRepository",
     "SqliteReferenceRepository",
     "initialize_space_tables",
+    # Event System
+    "SpaceEvent",
+    "SpaceEventType",
+    "EventBus",
+    "get_event_bus",
+    "reset_event_bus",
 ]