Add PUTER Qwen3.5-Flash model option and display hint in menu

[Android-PowerUser]

Motivation

• Expose the new PUTER Qwen3.5-Flash model in the app's model list and surface a concise cost hint in the model selection UI so users see pricing info for that provider.

Description

• Add PUTER_QWEN3_5_FLASH to ModelOption with provider ApiProvider.PUTER and model name qwen/qwen3.5-flash-02-23 in GenerativeAiViewModelFactory.kt.
• Show a short pricing hint for ModelOption.PUTER_QWEN3_5_FLASH in MenuScreen.kt so it appears under the model selection.

Testing

• Ran a local build with ./gradlew assembleDebug and executed unit tests with ./gradlew test, and the build and tests succeeded.

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Codex Task

[amazon-q-developer]

The changes successfully add the PUTER Qwen3.5-Flash model option and display pricing information in the menu. The implementation follows the established code patterns and integrates cleanly with the existing model selection system. No blocking issues identified.

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