`formatAge` is duplicated verbatim in cli/search.ts and mcp/tools.ts

[Deepam02]

Problem

The formatAge(recordedAt, nowMs) helper that renders compact age labels (12m, 5h, 3d, 2mo) exists as two identical copies:

• packages/agentctx/src/cli/search.ts:103 (exported)
• packages/agentctx/src/mcp/tools.ts:540 (private)

Both implementations are byte-for-byte equivalent (only the local variable name differs: ageMs vs ms). This is the same "duplicated helper" smell already tracked for describe(error) (#89) and the truncation helper (#90).

What done looks like

• Move formatAge into a single shared module (e.g. src/hooks/tokens.ts already holds shared formatting-style helpers, or a small src/format.ts) and import it from both cli/search.ts and mcp/tools.ts.
• Delete the two local copies.
• npm run check stays green.

Note

formatAge is also the subject of #37 (it never renders "1mo"). Consolidating into one copy first means that logic fix only has to be made in one place — coordinate with whoever picks up #37, or fold both into one PR.