feat: add official balance query for DeepSeek, StepFun, SiliconFlow, OpenRouter, Novita AI

Add a new "Official" (官方) template type in the usage query panel that
queries account balance via each provider's native API endpoint.
Follows the same zero-script pattern as Token Plan — Rust handles the
HTTP call, frontend auto-detects the provider from base URL.

Supported providers and endpoints:
- DeepSeek: GET /user/balance
- StepFun: GET /v1/accounts
- SiliconFlow: GET /v1/user/info (cn + com)
- OpenRouter: GET /api/v1/credits
- Novita AI: GET /v3/user/balance

src/config/constants.ts

@@ -10,6 +10,7 @@ export const TEMPLATE_TYPES = {
   NEW_API: "newapi",
   GITHUB_COPILOT: "github_copilot",
   TOKEN_PLAN: "token_plan",
+  BALANCE: "balance",
 } as const;
 
 export type TemplateType = (typeof TEMPLATE_TYPES)[keyof typeof TEMPLATE_TYPES];