feat: AI-Powered Journal Generation

[snehmatic]

This PR introduces the AI-Powered Journal Generation feature discussed in #106.

✨ Features

• Secure Token Storage: API tokens are encrypted (AES-GCM) before being stored in the database, configured via the web UI settings page.
• Provider Support: Connects directly with LLM providers (Google Gemini & OpenAI supported for V1) to auto-generate reflective summaries based on all tracked activity (focus sessions, habits, intents, tasks).
• CLI Generation: Generate and save summaries directly from the terminal (e.g. mindloop journal generate -w).
• Web UI Integration: A new AI Configuration section under Settings, and a convenient dropdown in the Journal page to auto-generate daily, weekly, or yearly entries.
• Context Aggregation: Uses the existing summary package to efficiently pre-aggregate large volumes of data to fit within standard model context windows.

🧪 Testing

• Added robust unit tests for the newly created crypto utility.
• Tested locally for successful integration across both CLI and the web server.

Fixes #106