feat(page-builder): add AI draft/apply/revert preview flow

[nooblemon-eth]

Summary

• Adds a draft/apply/revert UX flow so users can preview AI-generated page edits before committing them. AI mutations (AiCreatePageConfig, AiUpdatePageConfigSection, AiGeneratePageFromDescription) now snapshot Craft.js state, render the AI result as a read-only preview, and let the user apply or revert.
• Auto-save and Craft.js editing are blocked during preview to prevent partial persistence.
• Cancel during an in-flight mutation is safe — an abort guard prevents stale .then/.catch callbacks from transitioning state after revert.
• The ai_page_edit tool handler in InputChat validates payload schema explicitly and logs warnings on every invalid path instead of silently no-oping.

Key changes

Area	Files	What
State	store.ts	6 Jotai atoms + AIDraftPhase type + derived isAIDraftPreviewAtom
Hook	hooks/useAIPageEdit.ts	Orchestration: snapshot → mutation → preview → apply/revert, with cancelledRef abort guard
Bridge	hooks/ai-page-edit-bridge.ts	Module-level ref bridge (same pattern as use-safe-editor.ts)
Banner	panels/AIDraftBanner.tsx	Phase-aware banner: loading/previewing/error with contextual actions
Editor	Editor.tsx	Hook wiring, auto-save guard, actions.setOptions({ enabled }) toggle, banner render
Chat	InputChat.tsx	ai_page_edit tool handler with explicit schema guards + console.warn
Exports	panels/index.ts	Added AIDraftBanner

Test plan

• yarn test __tests__/page-builder/ — 242/242 passed, 11 files, 0 regressions
• yarn build — exit 0, no type errors
• Manual: open page builder → trigger AI edit via chat → verify loading banner → verify preview state → apply → confirm auto-save fires
• Manual: trigger AI edit → cancel during loading → confirm no error flash
• Manual: trigger AI edit → revert → confirm original state restored

🤖 Generated with Claude Code