Keep note titles visible across semantic zoom

[Yuqing (mydmdm)]

Summary

• render a persistent, non-shrinking title row in full-detail note cards
• account for title chrome in note auto-height geometry and invalidate stale measurements
• cover 300px/400px notes across full/minimal LOD plus constrained fixed-height behavior
• update note, auto-height, and canvas zoom architecture docs

Validation

• pnpm typecheck
• pnpm format
• pnpm lint:fix
• pnpm format:check
• pnpm --filter @huabu/shared exec vitest run src/canvas-engine/height/__tests__/height.test.ts src/canvas-engine/__tests__/createNodes.selection.test.ts
• pnpm --filter @huabu/web exec playwright test e2e/note-auto-height.spec.ts (8 passed)

Closes #81

[Yuqing (mydmdm)]

需要进一步讨论这个需求与在 note 正文中添加 H1 的区别