[K] Cut v3.0.0 release

[cbeaulieu-gt]

Parent epic: #273 · Spec: docs/superpowers/specs/2026-05-20-codex-pivot.md §10, §11 (#K)

Scope

Cut the v3.0.0 release marking the Codex-only end state.

Steps

1. Freeze v2 floating tag at the last Claude-era commit on main (do not force-update v2 once cutover lands)
2. Create v3.0.0 annotated tag at the post-cutover main HEAD
3. Move v3 floating tag to v3.0.0
4. Write GitHub Release notes against v3.0.0 documenting all breaking changes from spec §10:
   • CLAUDE_CODE_OAUTH_TOKEN removed; OPENAI_API_KEY required
   • All claude-*.yml reusable workflows renamed to codex-*.yml
   • GHCR overlay images retired (deletion in #L, +30 days from #M completion)
   • @claude verb router retired; use @codex via the App

Acceptance

• v3.0.0 tag exists and points to post-cutover commit
• v3 floating tag points to v3.0.0
• v2 tag frozen at pre-cutover commit (verifiable by git log v2)
• Release notes published with §10 breaking-change list

Depends on

• #J merged (consumer docs must be ready before tag is cut)
• All prior Phase 1 sub-issues (#A–#I) merged

🤖 Generated by Claude Code on behalf of @cbeaulieu-gt