feat(ui): editing and developer surfaces

[ubugeeei]

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

Outcome

Ship rich editing, code, terminal, in-place edit, and drawing surfaces with accessible fallbacks.

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

• Rich Text Editor: semantic model, toolbar, links, lists, tables, media, history, paste sanitation, collaboration adapters
• Markdown Editor: preview, source, extensions, sanitization, round-trip tests
• Code Editor and Diff Editor: highlighting, diagnostics, completion, search, minimap, textarea fallback
• Terminal and log viewer: ANSI, streaming, selection, search, copy, resize, screen-reader transcript
• In-place Editor and Cell Editor: commit/cancel, conflict, optimistic persistence
• Drag Handle, Sortable, Resize Handle, Selection Rectangle
• Signature Pad and drawing canvas: eraser, pressure adapter, export, keyboard-accessible alternative

Dependencies

Depends on #4892 and #4891. HTML-in-canvas host is #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

Contenteditable and textarea fallback dual trees. Terminal ANSI parsing tests. Drawing canvas hit-testing in browser mode.

Out of scope

Shortcut/history primitives and drag primitives are dependencies. HTML-in-canvas host belongs in next-gen.