feat(spaces): implement Phase 8 Git History Tracking

Implements optional git-based version control for information spaces:
- HistoryConfig model for configuring history tracking
- Commit, Branch, HistoryEntry, DiffResult models
- IHistoryBackend and IHistoryQuery interfaces
- GitHistoryBackend using git CLI for version control
- GitHistoryEventHandler for event-driven auto-commits
- HistoryEventCoordinator for managing space history
- HistoryQueryService for high-level history queries
- Automatic commits on DOCUMENT_ADDED/REMOVED/CONTENT_CHANGED events
- Support for:
  * Commit log with pagination and filtering
  * Diff between versions
  * File content at specific versions
  * Branch creation and switching
  * Version restoration
  * Uncommitted changes detection
- 43 comprehensive unit tests with git availability checks

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

markitect/spaces/__init__.py

@@ -83,6 +83,27 @@ from .composability import (
 )
 from .composability.service import CircularReferenceError
 
+# Phase 8: History Tracking (Optional)
+from .history import (
+    # Models
+    Commit,
+    Branch,
+    HistoryEntry,
+    DiffResult,
+    DiffLine,
+    DiffType,
+    HistoryConfig,
+    # Interfaces
+    IHistoryBackend,
+    IHistoryQuery,
+    # Implementations
+    GitHistoryBackend,
+    GitError,
+    GitHistoryEventHandler,
+    HistoryEventCoordinator,
+    HistoryQueryService,
+)
+
 __all__ = [
     # Models
     "InformationSpace",
@@ -130,4 +151,21 @@ __all__ = [
     "IAccessControlRepository",
     "SqliteSpaceReferenceRepository",
     "SqliteAccessControlRepository",
+    # History - Models
+    "Commit",
+    "Branch",
+    "HistoryEntry",
+    "DiffResult",
+    "DiffLine",
+    "DiffType",
+    "HistoryConfig",
+    # History - Interfaces
+    "IHistoryBackend",
+    "IHistoryQuery",
+    # History - Implementations
+    "GitHistoryBackend",
+    "GitError",
+    "GitHistoryEventHandler",
+    "HistoryEventCoordinator",
+    "HistoryQueryService",
 ]