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/schema/__init__.py

@@ -0,0 +1,72 @@
+"""
+Schema management modules for MarkiTect.
+
+This package contains the schema-related functionality:
+- Validator: Validate markdown documents against JSON schemas
+- Generator: Generate JSON schemas from markdown structures
+- Loader: Load schemas from markdown files with embedded JSON
+- Analyzer: Analyze schemas for rigidity issues
+- Refiner: Refine rigid schemas with loosening rules
+- Naming: Schema filename convention validation
+
+All modules are re-exported from their original schema_*.py locations
+for backward compatibility.
+"""
+
+from .validator import SchemaValidator
+from .generator import SchemaGenerator
+from .loader import (
+    MarkdownSchemaLoader,
+    SchemaLoaderError,
+    InvalidSchemaFormatError,
+    SchemaNotFoundError,
+)
+from .analyzer import (
+    SchemaAnalyzer,
+    SchemaAnalysisResult,
+    SchemaIssue,
+    IssueType,
+    IssueSeverity,
+)
+from .refiner import (
+    SchemaRefiner,
+    RefinementResult,
+    RefinementAction,
+)
+from .naming import (
+    validate_schema_filename,
+    suggest_valid_filename,
+    extract_schema_domain,
+    get_schema_version,
+    SchemaFilenameError,
+    SCHEMA_FILENAME_PATTERN,
+)
+
+__all__ = [
+    # Validator
+    "SchemaValidator",
+    # Generator
+    "SchemaGenerator",
+    # Loader
+    "MarkdownSchemaLoader",
+    "SchemaLoaderError",
+    "InvalidSchemaFormatError",
+    "SchemaNotFoundError",
+    # Analyzer
+    "SchemaAnalyzer",
+    "SchemaAnalysisResult",
+    "SchemaIssue",
+    "IssueType",
+    "IssueSeverity",
+    # Refiner
+    "SchemaRefiner",
+    "RefinementResult",
+    "RefinementAction",
+    # Naming
+    "validate_schema_filename",
+    "suggest_valid_filename",
+    "extract_schema_domain",
+    "get_schema_version",
+    "SchemaFilenameError",
+    "SCHEMA_FILENAME_PATTERN",
+]