Add multi-server 3x-ui registry with per-panel subscription URLs.

Admins can manage several 3x-ui panels by name and select which one issues invite/user configs via that server's /sub base URL.

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

db/connection.py

@@ -87,6 +87,12 @@ def init_schema():
             cur.execute(
                 "ALTER TABLE invite_links ADD COLUMN IF NOT EXISTS duration_days INTEGER NOT NULL DEFAULT 0"
             )
+            cur.execute(
+                "ALTER TABLE invite_links ADD COLUMN IF NOT EXISTS xui_panel_id TEXT NOT NULL DEFAULT ''"
+            )
+            cur.execute(
+                "ALTER TABLE user_connections ADD COLUMN IF NOT EXISTS xui_panel_id TEXT NOT NULL DEFAULT ''"
+            )
         conn.commit()
     _schema_ready = True
     logger.info('PostgreSQL schema ready')