[Webtoon study] Add phone, chat, status, and object insert components for webtoon storytelling

[realproject7]

Context

Several sample patterns rely on non-illustration inserts: phone screens, message/call UI, system/status cards, documents, clocks, signs, doors, buttons, and small object panels. These elements are cheap to produce, help scene transitions, and carry plot information without requiring a full illustration.

Required Changes

Add reusable webtoon insert components that can be created in the transition/interstitial editor and placed in the episode sequence:

• Phone message thread insert.
• Incoming/outgoing call insert.
• System/status notification insert.
• Document/note/card insert.
• Timer/countdown insert.
• Sign/location insert.
• Object close-up insert.
• Button/action UI insert.

These should render as stylized webtoon panels, not raw browser UI screenshots.

UX Requirements

• Users can choose insert type, enter short text, and preview it in the vertical sequence.
• Inserts can have genre skins: neutral, thriller-dark, modern-fantasy-system, romance-soft, slice-of-life-simple.
• Inserts must support export as final episode images or vector/composited panels.

Acceptance Criteria

• Inserts are first-class episode elements with predictable JSON.
• Preview and export match.
• Insert text is editable and not baked into generated art.
• Agents can request inserts during planning.
• No external copyrighted UI is copied.

Verification

• Render tests for each insert type.
• Browser test for create/edit/delete/reorder insert element.
• Export test confirms inserts appear in correct episode order.