[Webtoon study] Add semantic episode beat model and genre templates

[realproject7]

Context

The sample study shows that a webtoon episode needs a beat structure before it needs final images. Current cartoon episode planning still behaves too much like markdown/prose planning plus image cuts. We need a webtoon-native model that defines what each scroll segment is doing.

Required Changes

Add an episode beat model for cartoon stories. It should support, at minimum:

• hook: the first-scroll promise or disruption.
• baseline: ordinary world / status quo before the turn.
• incitingMoment: first event that changes the episode direction.
• escalation: repeated complication or pressure.
• reveal: new information, power, threat, romantic signal, or gag turn.
• transition: non-illustration connective tissue between illustrated moments.
• payoff: short-term emotional or plot payoff.
• endingTurn: final question, cliffhanger, loop, gag, or relationship complication.

Add genre presets derived from the abstract study patterns:

• Modern fantasy: deficit -> ability/system trigger -> proof of power -> institutional/social consequence -> repeatable reward loop.
• Thriller: normal family/school life -> uncanny detail -> silence/reaction -> threat reveal -> unresolved dread.
• Romance: loneliness or social setup -> accidental encounter -> attraction/confusion -> communication artifact -> relationship complication.
• Slice-of-life: title card -> repeated small situation -> escalating small misunderstanding -> compact gag/observation close.

Data Model

Extend cartoon episode metadata without breaking existing *.cuts.json files. Prefer additive fields:

• episodeBeats[]
• beatId on each cut/transition/text panel
• beatRole
• pacingWeight
• readerQuestion
• emotionalState
• genreFunction

Acceptance Criteria

• New cartoon episodes can be generated from a selected genre template.
• Existing stories load unchanged if beat metadata is absent.
• The episode preview can show beat names compactly without crowding the cut workspace.
• Agent instructions can consume the beat model when planning cuts.
• Tests cover migration/defaulting and at least four genre templates.

Verification

• Unit tests for default beat template generation.
• Regression test that old cartoon stories without beat metadata still open.
• A sample original episode plan shows hook, escalation, transition, payoff, and ending turn.