refactor: simplify prompt handling by removing TSX-related code and configurations

[plusplusoneplusplus]

Summary

This PR simplifies the prompt handling in AgentPanelProvider by removing TSX-related code and configurations, making the codebase cleaner and more maintainable.

Changes Made

Removed TSX Dependencies

• Removed imports for TsxRenderOptions, TsxRenderResult from prompt manager types
• Removed AgentPrompt component import
• Removed ChatMessage and DEFAULT_PRIORITIES imports

Simplified Configuration

• Removed enablePrioritization and fallbackToStringConcatenation flags from AgentPromptConfig
• Updated configuration to only include maxTokens and historyMessageCount

Streamlined Prompt Enhancement Logic

• Removed complex TSX-based prompt enhancement method enhanceParamsWithTsxPrompt
• Simplified enhanceParamsWithPrompt to use string concatenation approach
• Added support for optional user input (can use prompt alone or combined with user message)
• Improved prompt file path handling with direct reference support

Enhanced Prompt Handling

• Added variable detection logic to conditionally render prompts with variables
• Improved prompt content formatting with better system instruction labeling
• Added support for prompt-only mode (no user input required)
• Enhanced error handling for missing prompts

Code Cleanup

• Removed unused TSX message conversion utilities
• Removed complex conversation history formatting for TSX
• Simplified class documentation removing TSX references
• Reduced overall code complexity by 96 lines

Testing

• All existing functionality should work as before
• Prompt integration maintains backward compatibility
• Agent capabilities continue to be respected

Breaking Changes

None - this is a refactoring that maintains the same public API.

Related Issues

This addresses technical debt and simplifies the codebase for better maintainability.