Local semantic search

[bernoussama]

Summary

• Add local SQLite semantic search plumbing with sqlite-vec and optional sqlite-lembed support.
• Extend the CLI with local status, doctor, and embed commands, plus local setup flags.
• Refresh the CLI and MCP skill guidance to match the new local workflow.

Testing

• Added and updated unit tests for local semantic search, setup configuration, package metadata, and MCP tool coverage.
• Verified the CLI test suite for the local backend and ran TypeScript type-checking successfully.