feat: simplify clip prepare and export results

[FernandoAbishai]

Phase 7C.4 only.

This change:

• simplifies normal Clip Prepare through progressive disclosure
• keeps framing and captions directly accessible
• keeps technical export settings under Advanced
• keeps publishing copy explicitly optional
• improves creator-facing clip export completion/results
• preserves SRT fallback and existing retry/recovery contracts
• changes no backend, project schema, release files, or package version

Validation:

• focused Prepare/export smoke
• neighboring Clips workflow smokes
• all frontend smokes
• lint
• production frontend build
• git diff --check

Browser automation:

• not run because agent-browser is unavailable

Do not merge.

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