feat: implement MC domain filter proxy, API, dashboard

- proxy: asyncio TCP proxy with handshake parser, domain whitelist,
  transparent backend tunneling, SQLite logging, mtime hot reload
- api: FastAPI routes for config/domains/logs/status + restart trigger
- frontend: React + Vite NPM-style dashboard (dashboard/domains/logs/settings)
- nginx: reverse proxy for /api -> api:8000 and / -> frontend:3000
- docker-compose: full stack with shared data volume
- replace spec mc-domain-filter.md with README.md

nginx/nginx.conf

@@ -0,0 +1,41 @@
+events {}
+
+http {
+    include       /etc/nginx/mime.types;
+    default_type  application/octet-stream;
+    sendfile      on;
+
+    upstream mc_api      { server api:8000; }
+    upstream mc_frontend { server frontend:3000; }
+
+    server {
+        listen 80 default_server;
+        server_name _;
+
+        client_max_body_size 1m;
+
+        location /api/ {
+            proxy_pass         http://mc_api;
+            proxy_http_version 1.1;
+            proxy_set_header   Host              $host;
+            proxy_set_header   X-Real-IP         $remote_addr;
+            proxy_set_header   X-Forwarded-For   $proxy_add_x_forwarded_for;
+            proxy_set_header   X-Forwarded-Proto $scheme;
+        }
+
+        location = /health {
+            proxy_pass http://mc_api;
+        }
+
+        location / {
+            proxy_pass         http://mc_frontend;
+            proxy_http_version 1.1;
+            proxy_set_header   Upgrade           $http_upgrade;
+            proxy_set_header   Connection        "upgrade";
+            proxy_set_header   Host              $host;
+            proxy_set_header   X-Real-IP         $remote_addr;
+            proxy_set_header   X-Forwarded-For   $proxy_add_x_forwarded_for;
+            proxy_set_header   X-Forwarded-Proto $scheme;
+        }
+    }
+}