ai-assistant: Fix model selection issues

[skoeva]

These changes address some problems with model selection. The AI Assistant now:

• Uses the model selected in settings within the plugin UI
• Persists the chatbox and conversation history across model changes
• Cleans up sanitization of config inputs

Fixes: #364

[Copilot]

Pull request overview

This PR addresses model selection issues in the AI assistant by introducing a centralized resolveSelectedModel function and adding input sanitization for provider configurations. The changes aim to improve the robustness of model selection by prioritizing explicit model choices, falling back to saved configurations, and finally defaulting to provider-specific models.

Key Changes:

• Introduced resolveSelectedModel function to centralize model selection logic with fallback hierarchy
• Added sanitization of configuration values (API keys, endpoints, models) to handle trailing whitespace
• Modified history preservation behavior when switching providers (now appends instead of clearing)

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
ai-assistant/src/modal.tsx	Adds resolveSelectedModel function and updates model selection logic across initialization and provider switching; changes history handling to preserve chat history when switching configurations
ai-assistant/src/langchain/LangChainManager.ts	Implements sanitization logic for all configuration values to trim whitespace from strings before passing to AI provider clients

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

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[illume]

🎉 thanks!