[Webtoon study] Add storyboard rhythm map and pacing QA to episode preview

[realproject7]

Context

The study shows that episode quality depends on scroll rhythm: dense dialogue needs relief, action needs vertical impact, dread needs silence, romance needs reaction spacing, and slice-of-life needs compact timing. Current OWS preview shows content but does not help evaluate rhythm.

Required Changes

Add a storyboard rhythm map to the cartoon episode preview/edit workflow:

• A compact vertical minimap showing image cuts, text panels, transitions, and major beats.
• Per-element markers for dialogue density, silence, SFX, transition, and emotional intensity.
• Warnings for long runs of the same element type.
• A per-beat summary: hook, setup, escalation, reveal, payoff, ending.
• Click on minimap item jumps to that cut/transition.

Add pacing QA checks:

• No hook in first N scroll segments.
• Too many consecutive dialogue-heavy panels.
• Too many image cuts without transition/silence.
• Missing reaction shot after major reveal.
• Missing ending turn.
• Overuse of identical balloon style.
• Missing text-only or interstitial panels in dialogue-heavy episodes.

Acceptance Criteria

• Preview can show the whole episode structure without loading every full-size image at once.
• QA warnings are advisory, not publish blockers unless explicitly configured.
• Users can jump from a warning to the affected cut/transition.
• Checks are data-driven from the episode element model and overlay metadata.

Verification

• Unit tests for pacing QA rules.
• Browser test for minimap navigation.
• Original modern fantasy, thriller, romance, and slice-of-life test plans produce distinct rhythm maps.