[B2b] Add brain_search_feedback tool for agent self-reporting

[four-bytes-robby]

Purpose

Agents can report whether a search was helpful. Updates the most recent matching search_analytics row.

Design

Register tool brain_search_feedback in src/four-opencode-brain.ts:

args: {
  query: string,        // match to search_analytics row
  helpful: boolean,     // was the search helpful?
  used_results: boolean // did the agent use any results?
}

Logic:

• Find most recent search_analytics row where query matches (partial LIKE match)
• Update helpful, used_results columns
• Return { updated: true, id } or { updated: false, reason: "no matching search found" }

Acceptance

• Tool registered and callable
• Updates correct analytics row
• Idempotent (calling twice updates same row)
• Tests: feedback on existing search, feedback on non-existent query