Phase 9D: extract clip export controller

[FernandoAbishai]

Summary

• extract clip export/job orchestration from AIPanel into useClipExportController
• move transient export jobs/outputs, directory ownership, polling, cancel/retry, direct export, batch sequencing and manifest orchestration behind one vertical controller
• keep Review/Prepare, draft editing, AI discovery, publishing copy and UI composition in AIPanel
• preserve backend, project schema, provider contracts and 9C.3 lifecycle semantics

Preserved safety invariants

• durable status=exporting is claimed before the first /jobs/export await
• direct export and retry re-read the current durable draft
• batch re-reads every planned draft JIT and pauses if it was invalidated
• cancel does not terminalize or release busy before polling observes terminal state
• export folder remains frozen while busy
• runtime file capabilities remain transient only
• project v1 save/reopen behavior is unchanged

Architecture boundary

• AIPanel no longer owns clip export endpoints, polling, job/output state or batch stop state
• controller does not own AI provider, clip-metadata, publishing-copy or social-publishing orchestration

Validation

• all 22 frontend test:* scripts PASS
• npm run smoke:golden-creator-path PASS
• npm run lint PASS
• npm run build:frontend PASS
• git diff --check PASS
• two independent CURRENT blocker/high reviews: no blocker/high findings

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