refactor: remove lite variant, fix release workflow

- Remove all lite/full variant logic from frontend, API, shared constants,
  docs, and tests (single unified Docker image only)
- Replace single QEMU multi-arch Docker build with per-architecture native
  builds (amd64 + arm64) and manifest merge to fix disk space exhaustion
- Add disk cleanup step and per-platform build cache scopes
- Switch release trigger from push to workflow_dispatch
- Add GitHub issue templates and PR template

.gitignore

@@ -31,8 +31,6 @@ blob-report/
 
 # IDE / tool scratch
 .superpowers/
-.claude/
-CLAUDE.md
 docs/superpowers/
 PRD.md