feat: release ContentCloud v0.7.0

[wutongci]

Summary

• replace the V1/V2 runtime with the V3 workspace, submission, decision, snapshot, projection, delivery, and learning chain
• add V3 contracts, fixtures, Codex handoff, focused Web project console, and signed Plugin 0.7.0 metadata
• enforce atomic Submission transitions using the current revision and expected prior state
• replace cumulative migrations with the single 00001_v3_baseline.sql empty-database baseline

Verification

• go test -race ./...
• go vet ./...
• PostgreSQL 18 integration suite with CONTENTCLOUD_TEST_DATABASE_URL
• Web: 45 tests, TypeScript check, production build
• Plugin: deterministic evaluation, release validation, Ed25519 signature tests
• pnpm governance:v3
• npm package dry-run and launcher syntax check
• six CLI platform builds with gzip and SHA-256 verification

Breaking boundary

v0.7.0 supports a newly created V3 database only. It intentionally refuses databases carrying the V1/V2/0.6.0 migration history; production deployment requires a new database or a separately designed data migration.

Known acceptance limits

Real Codex Desktop host loading and full Browser/responsive acceptance remain documented post-release gates; deterministic contract and Browser safety tests do not claim those external-host checks.