chore: migrate fab project to kit 2.7.x

[sahil-noon]

Summary

Applies the fab-kit 2.6.6 → 2.7.0 migration and syncs project version stamps to the installed kit (2.7.1).

• Re-baseline memory indexes onto two-column form (2.6.6 → 2.7.0 migration): drops the Last Updated (git-date) column from every docs/memory/**/index.md. The date cell was a live git log projection (HEAD/branch-relative), which churned index cells back and forth across concurrent PRs. The index is now a pure function of content — branch-independent and byte-stable. Dated, change-attributed history still lives in each folder's log.md.
• Version stamps: fab_version → 2.7.1, fab/.kit-migration-version → 2.7.0.

Verification

• Re-baseline diff is purely the date-column drop; no Last Updated headers remain in any index.
• fab memory-index re-run is byte-stable ("Memory indexes already up to date").
• fab memory-index --check exits 0.

Note

The migration's pre-check probe writes an empty config.yaml, which the 2.7.x binary rejects for lacking fab_version — the probe aborts spuriously. Confirmed the running binary is genuinely 2.7.1 (≥ 2.7.0) by re-running the probe with a valid minimal config. Worth flagging upstream as a latent migration-probe bug.

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