Issue invite configs as subscription URLs with redeem-based lifetime.

Admin picks inbound once, sets duration in days from Get config, and configures the 3x-ui /sub base URL.

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

db/schema.sql

@@ -85,6 +85,7 @@ CREATE TABLE IF NOT EXISTS invite_links (
     xui_inbound_id INTEGER NOT NULL DEFAULT 0,
     password_hash TEXT,
     expires_at TIMESTAMPTZ,
+    duration_days INTEGER NOT NULL DEFAULT 0,
     note TEXT,
     created_at TIMESTAMPTZ
 );