feat: Convert LangChain implementation to new AIProvider interface

[jsonbailey]

Note

Refactors LangChain integration to an AIProvider-based provider with a new invoke flow and metrics, removes TrackedChat, and updates tests and configs.

• Core (LangChainProvider)
  • Convert to AIProvider subclass with constructor-held BaseChatModel, invokeModel, and getChatModel.
  • Add static create(aiConfig) and createLangChainModel factory using initChatModel and mapProvider.
  • Replace createTokenUsage/tracking helpers with createAIMetrics returning { success, usage }.
  • Keep convertMessagesToLangChain and provider mapping (e.g., gemini → google-genai).
• Removal
  • Delete LangChainTrackedChat and its exports; index.ts now exports only LangChainProvider.
• Tests
  • Update message imports to @langchain/core/messages; mock langchain/chat_models/universal.
  • Add tests for createAIMetrics and mapProvider; adjust expectations and formatting.
• Config
  • Update Jest config: use transform, broaden testMatch, simplify coverage settings, and add moduleFileExtensions.
  • Adjust ESLint tsconfig includes/excludes.

^{Written by Cursor Bugbot for commit fe29f8f. This will update automatically on new commits. Configure here.}

[cursor]

Bug: ESLint Include Pattern Uses Absolute Path

The include pattern ["/**/*.ts"] in tsconfig.eslint.json uses a leading slash, which makes it an absolute path from the filesystem root. This prevents ESLint from finding TypeScript files within the package, as it expects a relative path from the project directory.