Add full-text search to trace queries

[irparent]

Currently traces can only be filtered by agent_name, framework, and date range. Teams need to search trace content.

Goal: Add text search capability to get_traces and the dashboard.

Acceptance criteria:

• New search parameter on get_traces MCP tool
• Searches across: agent input, agent output, metadata values
• SQLite FTS5 for performant full-text search
• Dashboard search box on trace list page
• Search highlights in results

Resources:

• Storage adapter: src/storage/
• Architecture guide — Storage Design section