Add infrastructure changelog system to task-mcp

Implements session-aware infrastructure change tracking for CF-179.

Changes:
- New changelog.ts with 3 MCP tools:
  - changelog_add: Add infrastructure changes
  - changelog_since_session: Query changes since last session
  - changelog_list: Time-based fallback query
- Integrated with session-start command via MCP
- Database-first architecture (PostgreSQL on infra VM)
- Session-relative queries (not fixed time windows)

Database schema:
- infrastructure_changelog table (6 fields)
- Migrated 5 historical changes
- Indexes on date, session_id, created_at

Task: CF-179

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

src/tools/index.ts

@@ -389,6 +389,47 @@ export const toolDefinitions = [
     },
   },
 
+  // Infrastructure Changelog Tools
+  {
+    name: 'changelog_add',
+    description: 'Add infrastructure change entry for session awareness',
+    inputSchema: {
+      type: 'object',
+      properties: {
+        date: { type: 'string', description: 'Change date (YYYY-MM-DD)' },
+        title: { type: 'string', description: 'Short title (max 100 chars)' },
+        change_description: { type: 'string', description: 'What changed' },
+        impact: { type: 'string', description: 'Effects on existing infrastructure' },
+        actions_required: { type: 'string', description: 'Steps developers need to take (optional)' },
+        session_id: { type: 'string', description: 'Session that implemented change (optional)' },
+        task_ids: { type: 'array', items: { type: 'string' }, description: 'Related task IDs (optional)' },
+      },
+      required: ['date', 'title', 'change_description', 'impact'],
+    },
+  },
+  {
+    name: 'changelog_since_session',
+    description: 'Get infrastructure changes since last session for a project. Use at session start.',
+    inputSchema: {
+      type: 'object',
+      properties: {
+        project: { type: 'string', description: 'Project key (e.g., CF, VPN) to find last session' },
+      },
+      required: ['project'],
+    },
+  },
+  {
+    name: 'changelog_list',
+    description: 'List recent infrastructure changes by time period (fallback)',
+    inputSchema: {
+      type: 'object',
+      properties: {
+        days_back: { type: 'number', description: 'Days to look back (default: 7)' },
+        limit: { type: 'number', description: 'Max results (default: 20)' },
+      },
+    },
+  },
+
   // Project Lock Tools
   {
     name: 'project_lock',