feat: add web admin panel for node management

Add Flask panel with login, add/delete nodes, and share link copy.
Generate sing-box config from SQLite; add uninstall script and clean install flow.
Panel served at https://DOMAIN:8444 via nginx.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/nginx/panel.conf.template

@@ -0,0 +1,18 @@
+server {
+    listen 8444 ssl;
+    listen [::]:8444 ssl;
+    server_name __DOMAIN__;
+
+    ssl_certificate /etc/sing-box/certs/fullchain.pem;
+    ssl_certificate_key /etc/sing-box/certs/privkey.pem;
+    ssl_protocols TLSv1.2 TLSv1.3;
+
+    location / {
+        proxy_pass http://127.0.0.1:5080;
+        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;
+    }
+}