v1.5.0

chore(release): v1.5.0 — the remote Deployment release (#29)

Ship the Cloudflare Worker work (PRs #12-#28) as a published version.

- CHANGELOG.md: new, Keep-a-Changelog format. Thorough v1.5.0 entry
  (remote Deployment, D1 driver, gmail-rest adapter, OAuth, Job engine,
  Trigger rules + signed webhooks, A2A, seed path, freshness/auto-refresh,
  fixes, security posture, upgrade notes) plus back-filled 1.0.0-1.4.0.
- README: v1.5 status + feature TIP, v1.4 TIP demoted to historical, and
  the Documentation index now lists INSTALL-worker, WORKER-SEED,
  PLAN-worker, and the changelog.
- docs/PUBLISHING.md: the release is now one pushed tag end to end
  (release.yml -> npm + .mcpb + GitHub Release -> registry-publish.yml via
  OIDC). Documents the four-version-fields/three-files trap that left the
  registry entry pinned at 1.0.0 through v1.4.0, and adds post-release
  verification.
- Bump package.json, manifest.json, and BOTH server.json version fields to
  1.5.0.

427 tests, lint, and typecheck green.

Co-authored-by: al-unsoldgroup <al-unsoldgroup@users.noreply.github.com>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>