chore: 移除废弃的 relay_api_keys 表

Connect API Key 现在保存到 API Key Provider 系统，不再需要独立的 relay_api_keys 表

src-tauri/src/database/schema.rs

@@ -454,27 +454,6 @@ pub fn create_tables(conn: &Connection) -> Result<(), rusqlite::Error> {
     // ProxyCast Connect 相关表
     // ============================================================================
 
-    // Relay API Keys 表
-    // 存储中转商 API Key
-    // _Requirements: 4.1, 4.3_
-    conn.execute(
-        "CREATE TABLE IF NOT EXISTS relay_api_keys (
-            id TEXT PRIMARY KEY,
-            relay_id TEXT NOT NULL,
-            api_key TEXT NOT NULL,
-            name TEXT,
-            created_at TEXT NOT NULL,
-            updated_at TEXT NOT NULL
-        )",
-        [],
-    )?;
-
-    // 创建 relay_api_keys 索引
-    conn.execute(
-        "CREATE INDEX IF NOT EXISTS idx_relay_api_keys_relay_id ON relay_api_keys(relay_id)",
-        [],
-    )?;
-
     Ok(())
 }