Phase 5: Add immutable file headers to all protected files

Added protection headers to 9 critical files:

JSON Files (x-immutable-notice field):
- .dss/schema/api.schema.json
- .dss/schema/tokens.schema.json
- .dss/schema/components.schema.json
- .dss/schema/workflows.schema.json
- .dss/schema/guardrails.schema.json
- dss-claude-plugin/.mcp.json

YAML File (comment header):
- .dss-boundaries.yaml

Markdown File (HTML comment):
- API_SPECIFICATION_IMMUTABLE.md

Python File (docstring header):
- dss-mvp1/dss/validators/schema.py

Each header includes:
- Protection notice
- Reason for immutability
- Last modified date
- Bypass instructions (DSS_IMMUTABLE_BYPASS=1)

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

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

API_SPECIFICATION_IMMUTABLE.md

@@ -1,3 +1,14 @@
+<!--
+==================================================================================
+IMMUTABLE FILE - PROTECTED BY GIT PRE-COMMIT HOOK
+==================================================================================
+This file is protected by automated git hooks.
+Last Modified: 2025-12-09
+To update: Use 'DSS_IMMUTABLE_BYPASS=1 git commit -m "[IMMUTABLE-UPDATE] reason"'
+See "IMMUTABILITY NOTICE" section below for full change requirements.
+==================================================================================
+-->
+
 # Design System Server - API Specification (IMMUTABLE)
 
 **Document Version:** 1.0-IMMUTABLE