docs: add web ui migration inventory

Author: root

packages/web/src/components/ui/MIGRATION.md

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+# UI Component Migration Inventory
+
+| Component | Status | Legacy classes | Callers left | Last update |
+|---|---|---|---:|---|
+| Button | ⚫ not-started | `.btn .btn-*` | 31 | 2026-05-06 |
+| IconButton | ⚫ not-started | `.btn` icon-only | — | — |
+| Input | ⚫ not-started | `.input` | — | — |
+| Textarea | ⚫ not-started | `.input.textarea` | — | — |
+| Tag | ⚫ not-started | `.badge .badge-*` | — | — |
+| Badge | ⚫ not-started | `.badge` | — | — |
+| Pill | ⚫ not-started | `.settings-pill*` | — | — |
+| StatusDot | ⚫ not-started | token-backed dot patterns | — | — |
+| Kbd | ⚫ not-started | `kbd` | — | — |
+| Spinner | ⚫ not-started | `.animate-spin` | — | — |
+| Switch | ⚫ not-started | new | — | — |
+| Modal | ⚫ not-started | `.modal-overlay .modal-card .modal-*` | — | — |
+| ConfirmDialog | ⚫ not-started | modal convenience wrapper | — | — |
+| Toast | ⚫ not-started | `.toast*` | — | — |
+| Tooltip | ⚫ not-started | new | — | — |
+| ProgressBar | ⚫ not-started | `--progress-height` patterns | — | — |
+| Notice | ⚫ not-started | `.settings-page__notice*` | — | — |
+| EmptyState | ⚫ not-started | feature-specific empty state blocks | — | — |
+| Tabs | ⚫ not-started | tab / pill patterns across features | — | — |
+| SegmentedControl | ⚫ not-started | `.settings-pill*` | — | — |
+| Select | ⚫ not-started | `.input`, `.mobile-select-*` | — | — |
+| Popover | ⚫ not-started | new | — | — |
+| ActionMenu | ⚫ not-started | new | — | — |
+| Sheet | ⚫ not-started | mobile sheet shells | — | — |

packages/web/src/components/ui/README.md

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+# Coder Studio UI
+
+## 总则
+- 已落地的基础组件统一从 public barrel（当前文件路径为 `src/components/ui/index.ts`）引入，不允许深链到组件子路径。
+- 所有颜色、间距、字号、圆角、阴影、动效必须来自 `src/styles/tokens.css`。
+- 业务代码禁止新增 `btn btn-*`、`input` 这类旧式全局 className；未迁移的遗留调用点只允许原样保留，不允许扩散。
+- PC / 移动差异默认由 token 或共享内部逻辑解决，业务代码不直接写 `matchMedia`。
+
+## 已实现组件
+当前 phase 只会先落 `Button`。公共导出完成后，这里会改成可用组件列表。
+
+## 迁移状态
+见 `./MIGRATION.md`。