Scene editing, regeneration preview refresh and automatic idea lifecycle

[SubSchool]

Summary

• Default production playback to the newest immutable render and refresh completed regeneration without reloading the page.
• Add a scene editor with Gemini proposals, explicit save/cancel, and quoted confirmation for both regeneration entry points.
• Track queued/running/failed regeneration stages, preserve old media, protect concurrent operations and approved version history.
• Derive five idea stages from current production and publication; backfill existing ideas without changing media.
• Remove one-location UGC constraints and ask the whole-script critic to catch repetitive staging while preserving first-take identity anchors.

Verification

• Full local backend suite passed (182 tests); targeted regeneration suite re-run after history-approval safeguards.
• Ruff, web lint/typecheck and production build passed.
• Playwright CLI: mocked Gemini edit, save, cost confirmation, regeneration and automatic v1 → v2 playback verified on local fixtures; desktop/mobile modal screenshots inspected.
• No customer video regenerated or production prompts changed.