feat(ui): track UI package chain

[kattsushi]

Closes #1

PR Type

• Bug fix
• New feature
• Documentation only
• Code refactoring
• Maintenance/tooling
• Breaking change

Summary

• Adds reusable Solid UI package @os-copilot/ui with Nx/Vite build integration.
• Adds Zaidan/shadcn component baseline, mobile-first Storybook, Tailwind v4/Zaidan CSS foundation, all planned custom components, SSR/SPA/import smoke coverage, and explicit per-component subpath exports.
• This tracker PR is now the final integration branch for the completed child PR chain.

Chain Context

master
└── ✅ tracker #2: feat/ui-package
    ├── ✅ PR #3: scaffold package + shadcn routing
    ├── ✅ PR #4: Zaidan baseline + Storybook/CSS
    ├── ✅ PR #5: layout primitives + SSR/SPA verification
    ├── ✅ PR #6: component ergonomic subpath exports
    ├── ✅ PR #7: copy-id-button + marquee + Zaidan/Sonner toast
    └── ✅ PR #8: data-table + data-table-filters

PR	Scope	Base / Target	Status
#3	Scaffold package + shadcn routing smoke	feat/ui-package	Squash-merged into tracker
#4	Zaidan baseline/components + Storybook/CSS	feat/ui-package	Squash-merged into tracker
#5	Layout primitives + SSR/SPA/import smoke	feat/ui-package	Squash-merged into tracker
#6	Explicit ergonomic subpath exports	feat/ui-package	Squash-merged into tracker
#7	copy-id-button, marquee, Zaidan/Sonner toast	feat/ui-package	Squash-merged into tracker
#8	data-table and data-table-filters	feat/ui-package	Squash-merged into tracker

Changes

Area	Change
packages/ui	New Solid UI package with ESM exports, package-local Storybook, Vite/Nx targets, and tests.
packages/ui/src/components/ui/*	Zaidan component baseline plus all planned custom components.
packages/ui/src/stories/ui/*	Mobile-first Storybook stories for public components.
packages/ui/src/styles.css, packages/ui/src/styles/base.css	Tailwind v4 + Zaidan CSS/token foundation.
packages/ui/package.json	Root export, CSS export, shadcn source-routed exports, and explicit per-component subpath exports.
Workspace config	Nx Storybook integration, dependency catalog updates, and Storybook output ignore guards.

Deferred / Non-goals

• Automated visual regression tooling is deferred; current milestone uses Storybook build plus stories as the visual review surface.
• Publishing-ready dist-only exports remain out of scope; this package is private and source-routed for the monorepo milestone.
• Data table virtualization, server-side query orchestration, and advanced pagination are out of scope for this milestone.

Test Plan

• pnpm exec dprint check
• pnpm exec oxlint
• pnpm nx test ui --run
• pnpm nx typecheck ui
• pnpm nx build ui
• pnpm nx build-storybook ui
• pnpm nx typecheck web
• Judgment Day dual review before final tracker closure

Known non-blocking warnings

• Storybook emits unable to find package.json for @kobalte/core because Kobalte does not export ./package.json.
• Storybook reports large chunks due to the opt-in chart/ECharts story; chart remains absent from the root barrel and available via @os-copilot/ui/chart.
• Vitest/jsdom logs Window.scrollTo() method as not implemented; tests pass.

Contributor Checklist

• Linked an approved issue
• Added exactly one type:* label
• Ran shellcheck on modified scripts (not applicable; no shell scripts changed)
• Skills tested in at least one agent
• Docs updated if behavior changed
• Conventional commit format
• No Co-Authored-By trailers