feat(journl-agent): refactored system prompt with better practices and tool guidelines

[rmolinamir]

Description

This PR completely refactors the Journl agent's system prompt with cleaner structure, better tool guidelines, and improved user experience patterns.

Closes: #48

Key Improvements

Streamlined System Prompt Architecture

• Cleaner structure: Reorganized from verbose personality-driven prompt to focused, tool-centric approach
• Better tool documentation: Clear, actionable guidelines for each tool with specific use cases and examples
• Reduced verbosity: Eliminated unnecessary corporate AI language and filler phrases
• Context-aware behavior: Better integration of user state and editor context

Enhanced Tool Guidelines

• `manipulateEditor`: Clear guidelines for content generation with emphasis on markdown formatting, voice preservation, and actionable checklists
• Search tools: Better distinction between semantic journal search, semantic page search, and temporal search with clear use cases
• Navigation tools: Simplified navigation logic with UUID-based page navigation and date-based journal navigation
• Tool selection logic: Clear decision trees for when to use each tool

Improved User Experience

• Personalization: Added user name context to make interactions more personal
• Direct action: Emphasis on completing tasks immediately rather than asking clarifying questions
• Tone matching: Better guidelines for mirroring user communication style
• Contextual awareness: Enhanced understanding of active editors and highlighted text

[rmolinamir]

#66 broke CI, merging cause it's unrelated to this PR.