feat: redesign universe cast as character sheets

[atomantic]

Summary

Replace the Universe Cast's nested character-detail expanders with a gaming-style character sheet. Identity, portrait, and stats remain visible beside Attributes, Story, Appearance, and Voice pages containing open cards. Outfits, reference sheets, and LoRA tools live on Appearance.

Page selection is URL-backed and scoped to each character. Visited pages stay mounted to preserve pending rows and local drafts; production tools first load when their page is opened. Existing blur-to-save behavior, locks, and explicit generation actions remain intact. Portraits and field grids adapt to phone widths.

Test plan

• 81 tests passed across character editing, canon add/remove/picker workflows, thumbnail fallback behavior, and responsive grid conventions.
• Added interaction coverage for page links, retained pending rows, lazy voice loading, and locked fields/generation.
• Client production build and changed-file Biome lint passed.
• Browser verification with fictional cast data: all four pages at 1440, 768, and 360 pixels without horizontal overflow; desktop and phone screenshots inspected.