feat(mcp): add privacy-safe recall receipts

[cat0825]

Summary

Adds an optional includeReceipt flag to the MCP recall tool. When enabled, recall responses include a privacy-safe retrieval receipt in structuredContent.receipt.

The receipt helps users and maintainers debug cross-client memory retrieval without exposing raw memory text, raw queries, project names, transcripts, or private repository content.

Closes #985.

What changed

• Added includeReceipt to the MCP recall schema.
• Added createRetrievalReceipt() helper.
• Receipt includes:
  • hashed query
  • hashed project/container tag
  • hashed result IDs
  • hashed returned memory/chunk content
  • result count / total
  • score buckets
  • latency
  • MCP client name/version when available
  • profile static/dynamic counts when profile recall is used
• Added tests verifying raw private values are not exposed.

Validation

• bunx biome check --write apps/mcp/src/server.ts apps/mcp/src/retrieval-receipt.ts apps/mcp/src/retrieval-receipt.test.ts
• bunx vitest run src/retrieval-receipt.test.ts
• bun run --cwd apps/mcp build:ui

bun run check-types currently fails on existing unrelated @supermemory/tools type errors.