feat(settings): panel network proxy for the panel's own outbound requests

Add a panelProxy setting that routes the panel's self-initiated HTTP requests (geo updates, Xray version/core download, panel update check) through an admin-configured socks5/http(s) proxy, to bypass server-side filtering of GitHub/Telegram. The Telegram bot falls back to it when tgBotProxy is empty (socks5 only). New util/netproxy.NewHTTPClient builds the proxied client.

Also fix the Mixed-inbound SOCKS/HTTP share URLs that had host:port and user:pass in the wrong order, and consolidate the Telegram settings tab (move API server into the general tab, drop the empty Proxy & Server tab).

frontend/src/schemas/setting.ts

@@ -13,6 +13,7 @@ export const AllSettingSchema = z.object({
   webBasePath: absolutePath.optional(),
   sessionMaxAge: z.number().int().min(1).optional(),
   trustedProxyCIDRs: z.string().optional(),
+  panelProxy: z.string().optional(),
   pageSize: z.number().int().min(1).max(1000).optional(),
   expireDiff: nonNegativeInt.optional(),
   trafficDiff: nonNegativeInt.optional(),