feat: Add comprehensive system prompt management system.

[Emt-lin]

Summary

This PR introduces a comprehensive file-based system prompt management system that replaces the legacy single system prompt setting with a flexible, multi-prompt architecture.

Key Features

• File-Based Storage: System prompts are stored as .md files in a configurable folder
• CRUD Operations: Full create, read, update, delete, and duplicate functionality
• Clean Architecture: Repository → Manager → UIState → UI pattern with Jotai state management
• Automatic Migration: Seamlessly migrates existing userSystemPrompt from settings to file system
• Session & Global Prompts: Supports both session-level (temporary) and global default (persistent) prompt selection
• Rich UI: New management modal and chat settings integration with proper error handling and user feedback

Architecture Highlights

Core Components

1. SystemPromptManager (src/system-prompts/systemPromptManager.ts)

   • Singleton pattern for centralized CRUD operations
   • Manages file operations via Obsidian Vault API
   • Integrates with state management layer

2. State Management (src/system-prompts/state.ts)

   • Jotai-based reactive state with independent store
   • Dual API: React hooks (reactive) + imperative functions (non-React)
   • Session-level and persistent settings support

3. Migration System (src/system-prompts/migration.ts)

   • Automatic migration from legacy userSystemPrompt setting
   • User-friendly notification modal
   • Safe handling of existing files

4. Utilities (src/system-prompts/systemPromptUtils.ts)

   • File operations and validation
   • Frontmatter management
   • Name generation and conflict resolution

UI Components

• SystemPromptManagerModal: Full-featured management interface

  • Add new prompts
  • Edit existing prompts
  • Delete with confirmation
  • Duplicate prompts
  • Success/error notifications

• ChatSettingsPopover: Enhanced chat settings

  • System prompt selector dropdown
  • Session-level prompt override
  • Model parameter customization
  • Clear warnings for disabling builtin prompts

Breaking Changes

None. This PR includes automatic migration from the legacy userSystemPrompt setting to the new file-based system.

Test Plan

Functionality Testing

• [x] Create new system prompts via UI
• [x] Edit existing system prompts (title and content)
• [x] Delete system prompts with proper error handling
• [x] Duplicate system prompts with automatic name generation
• [x] Session-level prompt selection in chat settings
• [x] Global default prompt configuration in settings
• [x] Migration from legacy userSystemPrompt setting
• [x] File system operations (create, read, update, delete)
• [x] Frontmatter metadata handling
• [x] Error handling and user notifications (Notice)

Unit Tests

• [x] All existing tests pass
• [x] New test coverage: 1,671 lines across 4 test files
• [x] Migration scenarios tested
• [x] State management tested
• [x] CRUD operations tested
• [x] Utility functions tested

Integration Testing

• [x] Works with existing chat functionality
• [x] Compatible with all LLM providers
• [x] Session prompts reset correctly on new chat/load history
• [x] Global defaults persist across sessions

Screenshots

https://github.com/user-attachments/assets/6f30f847-6899-482d-8ef1-2670eab7d286

Migration Notes

For users upgrading to this version:

1. Existing custom system prompt (userSystemPrompt in settings) will be automatically migrated to a file named "Migrated Custom System Prompt" in the system prompts folder
2. The migrated prompt will be set as the global default automatically
3. A notification modal will inform users about the upgrade
4. No manual intervention required