Add proposal return-to-draft flows

[Cyber-preacher]

Why

Proposers need an explicit, understandable path from a failed or withdrawn proposal back to editable work without hiding its governance history.

What changed

• add a proposer-only Return to drafts action to live Proposal Pool pages
• explain the private-draft and history-preservation behavior in a confirmation dialog
• route successful returns into Proposal Wizard and reconcile stage races canonically
• show Continue editing only to owners of returned drafts
• label returned drafts by their server-projected source in My Drafts and draft detail
• add a reusable proposal-header action slot
• extend typed API contracts for owner-safe return projections

Validation

• yarn typecheck
• yarn test: 53 files, 238 tests passed
• yarn build
• Playwright complete suite: 105/105 passed
• focused return suite: 19/19 passed
• Light, Sky, Night, and Fire verified at 390, 768, 1024, and 1440 CSS pixels
• Prettier, diff, source, and production-bundle scans passed

Release safety

No runtime mock wiring, preview data, production-data change, or VPS deployment is included.