docs: add v0.1 release readiness notes

[ArcueidMP]

Summary

• Add v0.1 release-decision readiness notes
• Summarize Stage 9.2 manual E2E smoke results
• Summarize Stage 9.3 minimal CI scope and status
• Link the readiness notes from README
• Update docs/dev-log.md with PR ci: add stage 9 validation workflow #18 and Stage 9.4 handoff

Scope

Docs-only.

This PR does not:

• create a release
• tag v0.1
• create installers
• create GitHub Release binaries
• publish artifacts
• add auto-updater support
• add zip export
• add persistent settings
• add Runtime launch-from-Maker
• add rembg
• add cloud APIs
• add system tray
• add multi-pet support
• add plugin support
• add new animation features

Notes

The new document is for a human release decision. It is not release instructions and does not imply that installers or release binaries exist.

Verification

• git diff --check
• Bidi control character scan
• corepack pnpm typecheck

Optional:

• corepack pnpm build