feat(ui): layout, typography, and SVG

[ubugeeei]

Tracks this family from #3134. Experimental @vizejs/ui workstream.

Outcome

Ship layout, typography, avatar, image, and first-class SVG primitives that stay lightweight and CSS-first.

Authoring contract

• Public components are real .vue files. Handwritten render functions and JSX are not the public authoring model.
• Generated compiler output stays an internal artifact.
• Hover and completion must be enough to use the API without leaving the editor.
• Keep runtime script small. Prefer native HTML, CSS, and platform APIs.
• Extension is a first-class contract: parts, slots, CSS properties, and typed hooks.

Inventory

• Aspect Ratio, Separator, Spacer, Stack, Cluster, Grid, Container
• Resizable / Splitter: nested groups, persisted sizes, min/max, collapse, keyboard resize
• Scroll Area, Scroll Bar, Scroll Shadow, Scroll Top, overscroll affordance
• Card, Panel, Surface, Sheet, Hero, Item, List Item, description list
• App Shell, master-detail, split view, breakpoints, safe areas, viewport segments
• Typography: Heading, Text, Prose, Code, Kbd, Blockquote, List, truncation/clamp
• Avatar, Avatar Group, Icon, Icon Button
• Image, Image Compare, responsive picture
• SVG root, sprite, inline SVG, accessible title/desc, currentColor, and icon composer

Dependencies

Depends on #4893 and #4894. Charts are #4908. Graphics scenes are #4912.

Quality gates

This family is not done until it satisfies the parent definition of done in #3134:

• Canonical Vue SFCs with explicit <template>, <script setup lang="ts">, and scoped <style>
• kebab-case filenames for every public source, test, story, and fixture
• Every public prop, emit, slot, expose, CSS custom property, part, and data attribute documented; every option states @default
• Literal types for props, emits, slots, expose, and useTemplateRef
• Equivalent public contracts across DOM, SSR, and Vapor builds
• WCAG 2.2 AA, WAI-ARIA APG, keyboard, pointer, touch, focus, and dismissal where applicable
• LTR/RTL, locale, reduced motion, forced colors, and zoom
• SSR, hydration, deterministic IDs, Teleport, Suspense, islands, and no request-global state
• Colocated Vue Test Utils tests, Vitest browser-mode coverage, and Playwright visual regression
• Musea stories covering states, slots, parts, and presets
• Tree-shakable ESM subpath, exact sideEffects, and enforced bundle budgets
• Headless by default; visual style arrives only through opt-in presets

Testbed notes

Container query and logical-property CSS for the Lightning CSS pipeline. SVG title/desc a11y tests. Splitter keyboard tests.

Out of scope

Charts and signature canvas belong in data and editing. Three/WebGPU scenes belong in next-gen.