feat(tasks-ui): migrate the Tasks page to shadcn/ui (Tailwind v4 + radix, lazy chunk)

Visual base replacement for the Tasks page after the 'hard shadows make a
dense graph unreadable' review. Behaviour, hooks, aria labels and i18n are
unchanged; the base layer is not.

- FOUNDATION: Tailwind v4 wired into tsdown's css-inline plugin (theme +
  utilities ONLY — preflight is excluded because the plugin's stylesheet is a
  global <style data-plugin> tag and would repaint the host page), shadcn
  tokens bridged to --dsw-* so the DSH theme keeps flipping light/dark with no
  dark: overrides, cn() util, components.json for the CLI, src/client/ui/.
- COMPONENTS: shadcn's component source vendored into src/client/ui (button,
  card, badge, separator, input, textarea, tooltip, popover, dropdown-menu,
  scroll-area, collapsible, toggle-group, skeleton, spinner, empty) with a
  documented local diff: lucide-react replaced by host IconXxx (no new icon
  dep), shadow-* dropped from non-floating variants, unused variants pruned,
  and React.forwardRef restored on Button — the host runs React 18, where
  radix's Slot cannot hand a ref to a plain function component (dev warns,
  production silently mis-anchors the floating layer).
- SHADOWS: static panels are now hairline + surface tiers with hover:bg-muted;
  shadows exist only on floating layers. Settled nodes recede by ink
  (text-muted-foreground/foreground-3) instead of opacity.
- DENSITY: node cards widened 132 -> 150px with a two-line clamped title
  (13px text in a 132px card left ~7 CJK characters), reserved height 46 -> 60.
- CHUNK: the whole page (graph, tree, task window, board, drawer, shadcn/radix
  layer and its stylesheet) moved into the lazy 'tasks' chunk. Core bundle
  988.5 -> 835.6 KiB (-153 KiB); the 709.8 KiB UI payload loads only when the
  Tasks tab opens.
- MODEL: workflow members whose childId is already a real node elsewhere are
  no longer synthesized into a duplicate id (React keys/edges), with a
  last-resort per-id dedupe.
- GUARDS: tests/ui-foundation.spec.ts, tests/ui-bundle.spec.ts (core/chunk
  split + size budget + no preflight/oklch/lucide), tests/ui-shadows.spec.ts,
  extended tests/theme.spec.ts (no colour literal / palette class in
  src/client/ui/** and the migrated files).
- REVIEW FIXES: portal popovers re-scoped under .dsw-tasks, graph loading
  state, 11px floor, error nodes no longer tint a whole border, TeamBoard's
  delete item is neutral (the window owns the two-step confirm).

Verified: typecheck / lint / 136 files 1502 tests / build bundle assertions /
mount e2e 7-7; browser harness 65-65 checks with 0 console errors.

tests/tasks-model.spec.ts

@@ -191,3 +191,44 @@ describe('tasksEdges', () => {
     expect(kindOf('m1')).toBe('workflow')
   })
 })
+
+describe('buildTasksModel: duplicate workflow members', () => {
+  it('never synthesizes a second node for a member another parent already lists', () => {
+    // `m1` is a real child of `a`, but a run started by `root` names it as a
+    // member — the node must stay single (React keys / edge map depend on it)
+    // and the run simply does not duplicate it on the canvas.
+    const audit = run({
+      originSessionId: 'root',
+      phases: [{ title: '侦察', members: [{ seq: 1, label: 'm1', childId: 'm1', outcome: 'completed' }] }],
+    })
+    const model = buildTasksModel(input({
+      catalogs: {
+        root: catalog([child('a')]),
+        a: catalog([child('m1', { activity: 'inactive' })]),
+      },
+      byId: { root: summary('root'), a: summary('a'), m1: summary('m1') },
+      runs: [audit],
+      folded: false,
+    }))
+    const ids = model.map(node => node.id)
+    expect(ids.filter(id => id === 'm1')).toHaveLength(1)
+    expect(new Set(ids).size).toBe(ids.length)
+    // The real node keeps its catalog parent.
+    expect(model.find(node => node.id === 'm1')?.parentId).toBe('a')
+  })
+
+  it('still synthesizes a member no catalog knows', () => {
+    const audit = run({
+      originSessionId: 'root',
+      phases: [{ title: '侦察', members: [{ seq: 1, label: 'ghost member', childId: 'ghost' }] }],
+    })
+    const model = buildTasksModel(input({
+      catalogs: { root: catalog([]) },
+      byId: { root: summary('root') },
+      runs: [audit],
+      folded: false,
+    }))
+    const ghost = model.find(node => node.id === 'ghost')
+    expect(ghost).toMatchObject({ parentId: 'run:run-1', synthesized: true })
+  })
+})