Migrate Trellis workflow to YAML manifest

[yongchangwang-gt]

Summary

• Replace the monolithic .trellis/workflow.md guide with .trellis/workflow.yaml plus .trellis/workflow/** markdown body files.
• Add shared workflow model loaders for Python/OpenCode/Pi runtime consumers, and update CLI init/update templates, hooks, specs, bundled skills, and regression tests.
• Add bilingual i18n support for the affected CLI/template surfaces.
• Bump @mindfoldhq/trellis to 0.5.21 and restore published 0.6.0-beta.22, 0.6.0-beta.23, and 0.6.0-rc.0 migration manifests so continuity checks stay green.

Verification

• pnpm lint
• pnpm typecheck
• pnpm test
• node scripts/check-manifest-continuity.js from packages/cli
• node scripts/check-i18n.js --release from packages/cli

Previous targeted verification

• python3 -m py_compile on updated Python runtime/hooks/templates
• node --check on updated OpenCode files
• targeted CLI template/update/regression Vitest suites
• pnpm --filter @mindfoldhq/trellis build
• smoke-tested get_context.py phase rendering plus Codex workflow-state/session-start hooks