🤖 feat: gemini-3.1-flash-lite-preview Window & Pricing (#12043)

* 🤖 feat: `gemini-3.1-flash-lite-preview` Window & Pricing

- Updated `.env.example` to include `gemini-3.1-flash-lite-preview` in the list of available models.
- Enhanced `tx.js` to define token values for `gemini-3.1-flash-lite`.
- Adjusted `tokens.ts` to allocate input tokens for `gemini-3.1-flash-lite`.
- Modified `config.ts` to include `gemini-3.1-flash-lite-preview` in the default models list.

* chore: testing for `gemini-3.1-flash-lite` model, comments

- Updated `tx.js` to include cache token values for `gemini-3.1-flash-lite` with specific write and read rates.
- Enhanced `tx.spec.js` to include tests for the new `gemini-3.1-flash-lite-preview` model, ensuring correct rate retrieval for both prompt and completion token types.

api/models/tx.js

@@ -201,6 +201,7 @@ const tokenValues = Object.assign(
     'gemini-3': { prompt: 2, completion: 12 },
     'gemini-3-pro-image': { prompt: 2, completion: 120 },
     'gemini-3.1': { prompt: 2, completion: 12 },
+    'gemini-3.1-flash-lite': { prompt: 0.25, completion: 1.5 },
     'gemini-pro-vision': { prompt: 0.5, completion: 1.5 },
     grok: { prompt: 2.0, completion: 10.0 }, // Base pattern defaults to grok-2
     'grok-beta': { prompt: 5.0, completion: 15.0 },
@@ -331,8 +332,10 @@ const cacheTokenValues = {
   'kimi-k2-0711-preview': { write: 0.6, read: 0.15 },
   'kimi-k2-thinking': { write: 0.6, read: 0.15 },
   'kimi-k2-thinking-turbo': { write: 1.15, read: 0.15 },
-  // Gemini 3.1 models - cache read: $0.20/1M (<=200k), cache write: standard input price
+  // Gemini 3.1 Pro - cache write: $2.00/1M, cache read: $0.20/1M
   'gemini-3.1': { write: 2, read: 0.2 },
+  // Gemini 3.1 Flash-Lite - cache write: $0.25/1M, cache read: $0.025/1M
+  'gemini-3.1-flash-lite': { write: 0.25, read: 0.025 },
 };
 
 /**