feat: complete schema-evolution topic with ADR schema and markdown support

This commit closes the schema-evolution topic (260105) by adding the final
deliverable (ADR schema) and fixing markdown schema support across commands.

**ADR Schema Created**:
- Comprehensive Architecture Decision Record validation schema
- 12 section classifications (7 required, 2 recommended, 2 optional, 3 improper/discouraged)
- Content pattern validation for ADR formatting rules (status dates, decision statements, rationale structure)
- Quality metrics for completeness (word counts, sentence counts)
- Follows title case naming convention (Status, Context, Decision, etc.)

**Markdown Schema Support Fixed**:
- Fixed `markitect validate` command to support .md schemas
  - Added load_schema_from_path() for both .json and .md files
  - Updated structural and semantic validation to use schema dict
- Fixed `markitect generate-stub` command to support .md schemas
  - Uses load_schema_from_path() instead of direct JSON loading
- Created DocumentWrapper class in semantic_validator.py
  - Extracts headings from AST tokens (heading_open, inline)
  - Provides get_headings_by_level() interface expected by validators
  - Enables section validation to work with real documents

**Topic Closure**:
- Updated SCHEMA_EVOLUTION_WORKPLAN.md with completion summary
  - Phases 1-3: 100% complete (via Schema-of-Schemas and Semantic Validation)
  - Phase 4: Deferred as future enhancement (15-20 sessions)
  - Phase 5: 70% complete (docs done, CI/CD templates deferred)
- Created DONE.md with comprehensive task checklist
- Generated ADR template stub (examples/templates/adr-template.md)
- Moved topic from roadmap/ to history/260105-schema-evolution/

**Files Changed**:
- markitect/cli.py: Added markdown schema support to validate and generate-stub
- markitect/semantic_validator.py: Added DocumentWrapper class for AST parsing
- markitect/schemas/adr-schema-v1.0.md: New ADR validation schema (560 lines)
- examples/templates/adr-template.md: Generated ADR template stub
- history/260105-schema-evolution/: Moved completed topic to history

**Status**: Schema evolution topic successfully closed with ADR schema as final deliverable.
All schema commands now support markdown schemas. Section validation working correctly.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

markitect/cli.py

@@ -1559,16 +1559,20 @@ def validate(config, file_path, schema, schema_json, quiet, detailed_errors, err
             click.echo("Error: Specify exactly one schema source (--schema or --schema-json)", err=True)
             sys.exit(1)
 
+        # Load schema dict (supports .json and .md)
+        schema_dict = None
+        if schema:
+            from .semantic_validator import load_schema_from_path
+            schema_dict = load_schema_from_path(schema)
+            schema_source = f"schema file: {schema}"
+        elif schema_json:
+            schema_dict = json.loads(schema_json)
+            schema_source = "provided JSON schema"
+
         # Perform validation (with or without detailed errors)
         if detailed_errors:
             # Use detailed error reporting for Issue #8
-            if schema:
-                error_collector = validator.validate_file_with_errors_file(file_path, schema)
-                schema_source = f"schema file: {schema}"
-            else:
-                error_collector = validator.validate_file_with_errors_string(file_path, schema_json)
-                schema_source = "provided JSON schema"
-
+            error_collector = validator.validate_file_with_errors(file_path, schema_dict)
             is_valid = not error_collector.has_errors()
 
             # Output detailed errors
@@ -1589,12 +1593,7 @@ def validate(config, file_path, schema, schema_json, quiet, detailed_errors, err
 
         else:
             # Use simple boolean validation (original Issue #7 functionality)
-            if schema:
-                is_valid = validator.validate_file_against_schema_file(file_path, schema)
-                schema_source = f"schema file: {schema}"
-            else:
-                is_valid = validator.validate_file_against_schema_string(file_path, schema_json)
-                schema_source = "provided JSON schema"
+            is_valid = validator.validate_file_against_schema(file_path, schema_dict)
 
             # Output results
             if quiet:
@@ -1613,12 +1612,9 @@ def validate(config, file_path, schema, schema_json, quiet, detailed_errors, err
 
         # Semantic validation (if enabled and schema has x-markitect extensions)
         semantic_report = None
-        if semantic and schema:
+        if semantic and schema_dict:
             try:
-                from .semantic_validator import SemanticValidator, load_schema_from_path
-
-                # Load schema (supports .md and .json)
-                schema_dict = load_schema_from_path(schema)
+                from .semantic_validator import SemanticValidator
 
                 # Check if schema has x-markitect extensions
                 has_extensions = ('x-markitect-sections' in schema_dict or
@@ -2550,10 +2546,9 @@ def generate_stub(config, schema_file, output, style, title):
         generator = StubGenerator()
         associated_files = AssociatedFilesManager()
 
-        # Load schema and generate stub content
-        import json
-        with open(schema_file, 'r') as f:
-            schema = json.load(f)
+        # Load schema (supports .json and .md)
+        from .semantic_validator import load_schema_from_path
+        schema = load_schema_from_path(schema_file)
 
         stub_content = generator.generate_stub_from_schema(
             schema, placeholder_style=style, title=title, schema_file_path=schema_file