Add search functionality for conversations and transcripts

[DebjyotiRay]

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name: Add search functionality for conversations and transcripts

Summary of Changes

Search functionality that enables users to search across their conversation history, including both AI messages and audio transcripts. The feature provides real-time search with keyword highlighting, session grouping, and direct navigation to relevant conversations.

Related Issue

• Closes [BUG] Search returns nothing #145

Key Features Added:

• Real-time Search: Search as you type across all stored conversations
• Multi-source Search: Searches both AI messages and audio transcripts
• Keyword Highlighting: Search terms are highlighted in yellow in preview snippets
• Direct Navigation: Click any result to jump directly to the session details

Contributor's Self-Review Checklist

Please check the boxes that apply. This is a reminder of what we look for in a good pull request.

• I have read the CONTRIBUTING.md document.
• My code follows the project's coding style and architectural patterns as described in DESIGN_PATTERNS.md.
• I have added or updated relevant tests for my changes. (Note: No unit tests required per CONTRIBUTING.md)
• I have updated the documentation to reflect my changes (if applicable).
• My changes have been tested locally and are working as expected.

Additional Context (Optional)