feat: implement mcpd core server framework with Fastify

Add Fastify server with config validation (Zod), health/healthz endpoints,
auth middleware (Bearer token + session lookup), security plugins (CORS,
Helmet, rate limiting), error handler, audit logging, and graceful shutdown.
36 tests passing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.taskmaster/tasks/tasks.json

@@ -158,7 +158,7 @@
           "1",
           "2"
         ],
-        "status": "pending",
+        "status": "done",
         "subtasks": [
           {
             "id": 1,
@@ -220,7 +220,8 @@
             "testStrategy": "TDD for all components: error handler HTTP codes, audit middleware creates records, graceful shutdown handles SIGTERM.",
             "parentId": "undefined"
           }
-        ]
+        ],
+        "updatedAt": "2026-02-21T04:21:50.389Z"
       },
       {
         "id": "4",
@@ -730,9 +731,9 @@
     ],
     "metadata": {
       "version": "1.0.0",
-      "lastModified": "2026-02-21T04:17:17.744Z",
+      "lastModified": "2026-02-21T04:21:50.389Z",
       "taskCount": 24,
-      "completedCount": 3,
+      "completedCount": 4,
       "tags": [
         "master"
       ]