[Webtoon study] Add webtoon lettering and transition QA checklist before export

[realproject7]

Context

Manual review is still needed before export, but the app can catch many obvious webtoon production mistakes: unstyled default bubbles, repeated balloon shapes, bubbles covering faces, missing transitions, unreadable text, excessive dialogue density, and ending without a turn.

Required Changes

Add a cartoon episode QA checklist before final export/upload:

• Bubble readability: font size, contrast, fit, overflow.
• Bubble tone coverage: non-default style used where tone metadata requires it.
• Tail/target sanity: tails point toward intended speaker or are marked narration/thought/offscreen.
• Safe-zone check: overlays avoid faces and key objects when possible.
• Transition coverage: scene/time changes have explicit transition element or establishing cut.
• Dialogue density: too many lines in one viewport gets warning.
• Silence/reaction checks after major reveal.
• Ending turn present.
• Publish-specific checks remain separate from craft warnings.

UX Requirements

• Checklist should be compact and actionable.
• Each warning should jump to the relevant cut/transition.
• Warnings should not block export unless they affect technical validity.

Acceptance Criteria

• Checklist runs from episode data, overlays, and element sequence.
• Users can dismiss advisory warnings per episode.
• Export still blocks hard technical failures like missing final images or invalid overlays.
• Tests cover at least 10 QA rules.

Verification

• Unit tests for QA rules.
• Browser test for warning -> jump target.
• Original test story intentionally triggers and then resolves warnings.