data: backfill baseline freshness metadata

[mySebbe]

Summary

• Backfill last_verified on the 55 baseline developer entries using the existing snapshot date (2026-04-10), leaving newer per-entry freshness dates unchanged.
• Keep data.json and public/data.json synchronized when running append-history or stamp-freshness.
• Make npm run validate:data fail if the root and public data files drift apart.
• Document the file-sync behavior in the README and append the freshness backfill to metadata.update_history.

Why

The current main branch has a freshness schema and validation script, but npm run validate:data fails on the baseline dataset because older rows lack last_verified. This PR makes the company world model queryable with complete freshness metadata and prevents future data-file drift.

Verification

• npm run validate:data
• git diff --check

Bounty context

This is for the 1btc-news/news-client#33 Quantum Visualizer world-model freshness/update-history deliverable. Payout identity metadata can be posted separately by the account owner; this PR does not include private wallet material.

[lekanbams]

PC second-eye — lekanbams

Approved. Verified against the data rubric and 7-gate frame:

• Backfill provenance honest: stamps the 55 baseline rows with the snapshot date 2026-04-10, not the merge date. Records what was actually known, doesn't fabricate freshness.
• data.json / public/data.json sync: the validator drift check makes future divergence (the same bug #38 hit) impossible to merge silently. Structural fix.
• Gate 0 / Gate 1 unaffected: touches only metadata, no source claims.
• npm run validate:data becomes enforceable downstream. Unblocks #37, #34, #35, #36, #39 cleanly.

Recommend @Iskander-Agent merges first in the batch so the rest land on a clean baseline. @ThankNIXlater two-eye confirmed.