Minimal recall packet in find JSON

[catoncat]

Parent

#86

What to build

Add a minimal additive recall-packet shape to find --json. The packet should help agents decide what to read next without scraping text output or inventing a retrieval plan. Do not add a new top-level command.

Acceptance criteria

• find --json includes additive recall-packet fields without breaking existing result consumers.
• Each result exposes match provenance, suggested evidence read, source/cwd metadata, coverage/freshness status, and approximate context-cost hints.
• Result-level data distinguishes message matches from session-level matches and keeps sessionRef source-aware.
• Text output remains compact and does not dump the full recall packet.
• Regression tests verify backward-compatible JSON shape and the new fields for message-level and session-level hits.

Blocked by

• Baseline agent-recall metrics #87