feat(spaces): implement Phase 0-1 of Information Space Service

Phase 0 - Project Organization:
- Create docs/PROJECT_STRUCTURE.md documenting codebase layout
- Create markitect/core/ with parser, serializer, document_manager, workspace
- Create markitect/schema/ consolidating 6 schema_*.py modules
- Create markitect/storage/ with database module
- Maintain backward compatibility via re-exports from original locations
- Add docs/roadmap/information-space-service/ with README and WORKPLAN

Phase 1 - Foundation (Weeks 1-3):
- Week 1: Core domain models (InformationSpace, SpaceDocument, SpaceConfig,
  SpaceMetadata, SpaceVariable, TransclusionReference, SpaceStatus)
- Week 2: Repository layer with interfaces (ISpaceRepository,
  IDocumentAssociationRepository, IVariableRepository, IReferenceRepository)
  and SQLite implementations with foreign key cascade deletes
- Week 3: SpaceService orchestration layer with full CRUD, document,
  variable, and reference tracking operations

Test coverage: 124 tests (25 model + 63 repository + 36 integration)

Capabilities delivered:
- CAP-001: InformationSpace entity with lifecycle management
- CAP-002: SpaceRepository CRUD with SQLite backing
- CAP-003: Document-Space associations with path-based organization
- CAP-004: Space metadata and configuration schemas
- CAP-005: Database schema with migrations

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

markitect/spaces/__init__.py

@@ -0,0 +1,76 @@
+"""
+Information Spaces package for MarkiTect.
+
+This package provides the Information Space abstraction, enabling:
+- First-class space entities with identity, metadata, and lifecycle
+- Event-driven change tracking and notifications
+- Persistent transclusion context with cross-space references
+- HTML rendering with caching and theme support
+- Bidirectional directory synchronization
+- Composable space hierarchies
+
+Package Structure:
+    - models: Core domain models (InformationSpace, SpaceDocument, SpaceConfig)
+    - events: Event system (SpaceEvent, EventBus, handlers)
+    - repositories: Data access layer (ISpaceRepository, SqliteSpaceRepository)
+    - transclusion: Persistent transclusion context and reference tracking
+    - rendering: Space rendering (HTML, themes)
+    - sync: Directory synchronization (export, import, bidirectional)
+    - services: Business logic (SpaceService)
+    - history: Optional git-based version control
+
+Usage:
+    from markitect.spaces import SpaceService, InformationSpace
+
+    service = SpaceService()
+    space = await service.create_space("my-docs")
+    await service.add_document(space, "/intro.md", content="# Intro")
+    await service.render(space, output_dir="./html/")
+"""
+
+# Phase 1: Foundation
+from .models import (
+    InformationSpace,
+    SpaceDocument,
+    SpaceConfig,
+    SpaceMetadata,
+    SpaceVariable,
+    TransclusionReference,
+    SpaceStatus,
+)
+from .services import SpaceService
+from .repositories import (
+    ISpaceRepository,
+    IDocumentAssociationRepository,
+    IVariableRepository,
+    IReferenceRepository,
+    SqliteSpaceRepository,
+    SqliteDocumentRepository,
+    SqliteVariableRepository,
+    SqliteReferenceRepository,
+    initialize_space_tables,
+)
+
+__all__ = [
+    # Models
+    "InformationSpace",
+    "SpaceDocument",
+    "SpaceConfig",
+    "SpaceMetadata",
+    "SpaceVariable",
+    "TransclusionReference",
+    "SpaceStatus",
+    # Services
+    "SpaceService",
+    # Repository Interfaces
+    "ISpaceRepository",
+    "IDocumentAssociationRepository",
+    "IVariableRepository",
+    "IReferenceRepository",
+    # SQLite Implementations
+    "SqliteSpaceRepository",
+    "SqliteDocumentRepository",
+    "SqliteVariableRepository",
+    "SqliteReferenceRepository",
+    "initialize_space_tables",
+]