🐛 fix: match Nano Banana 2 Lite model id to NanoBanana icon

The NanoBanana regex required flash/pro to be immediately followed by
`-image-preview`, so `gemini-3.1-flash-lite-image` (Nano Banana 2 Lite)
fell through to the generic Gemini icon.

src/features/modelConfig.ts

@@ -175,7 +175,7 @@ export const modelMappings: ModelMapping[] = [
     keywords: [
       'gemini-3.1-flash-image-preview',
       'gemini-3-pro-image-preview',
-      'gemini-\\d+(?:\\.\\d+)?-(?:flash|pro)-image-preview$',
+      'gemini-\\d+(?:\\.\\d+)?-(?:flash(?:-lite)?|pro)-image(?:-preview)?',
       'nanobanana',
       'nano-banana',
     ],