feat: release ContentCloud v0.6.0

[wutongci]

Summary

• add browser-confirmed PKCE bootstrap authorization with live progress and deterministic recovery actions
• add local prerequisite checks, redacted diagnostics, onboarding documentation, and PostgreSQL RLS persistence
• publish contentcloud-video-production 0.6.0 metadata and synchronize all version sources
• preserve production compatibility through migration 00019 without modifying published migrations

Validation

• make check
• go test -race ./... -count=1 with an isolated real PostgreSQL database
• pnpm evaluate:plugin (8 scenarios)
• pnpm --dir web test (21 tests)
• node --check packages/contentcloud/bin/contentcloud.js
• six-platform CLI cross-build, gzip integrity, and SHA-256 verification

Review

• pre-landing review completed; two data-consistency findings fixed and regression-tested
• design review lite completed with no findings
• docs/roadmap/v3 remains intentionally excluded as concurrent unrelated work