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.

src/client/chunks/tasks.tsx

@@ -0,0 +1,20 @@
+/**
+ * Lazy chunk entry: the whole Tasks page (workflow graph + tree, task window,
+ * team board, jobs drawer) together with the vendored shadcn/ui component set
+ * it renders. Built as `lib/client-tasks.js` and registered under
+ * `dsh-better-sidebar/tasks` — fetched only when the Tasks tab is first
+ * opened (see chunk-loader.ts and docs/plans/2026-08-12-lazy-chunks-design.md).
+ *
+ * Why it is a chunk: the shadcn/radix/tailwind-ui layer costs ~430 KiB raw
+ * (radix primitives + floating-ui + tailwind-merge + the vendored components),
+ * and README's "startup pulls only the core bundle" contract must hold for
+ * every user who never opens the Tasks tab. Never import this module (or the
+ * page modules it re-exports) from the core bundle.
+ */
+// The Tailwind sheet (theme bridge + compiled utilities) ships WITH the
+// chunk: it styles this page only, so the core bundle stays free of the
+// UI-layer payload and the host page never receives the stylesheet until a
+// reader opens the Tasks tab.
+import '../ui/theme.css'
+
+export { SubagentView } from '../SubagentView.tsx'