feat(ui): improve mobile kanban view (#400)

* feat(ui): add responsive layouts to swimlane kanban content

Mobile gets swipeable columns with tab navigation and touch-friendly
drag sensors. Tablet gets 2-column horizontal scroll with snap.
Desktop keeps the existing CSS grid layout.

* feat(ui): add mobile task sheet and search bar components

Bottom sheet (vaul Drawer) for task preview with Edit/Delete/Open Session
actions. Compact search bar component for filtering tasks on mobile.

* feat(ui): wire mobile components into kanban board

Integrate MobileFab, MobileSearchBar, and MobileTaskSheet into the
kanban board. Skip desktop preview panel on mobile — card taps open
a bottom sheet instead of navigating directly.

* refactor(ui): optimize swimlane container for mobile

Hide swimlane headers for single workflow on mobile, remove horizontal
padding on small screens. Extract filterTasks and WorkflowItem to keep
the main component under the line limit.

* test: add mobile kanban E2E tests

8 Playwright tests covering mobile layout, FAB, search, column tabs,
bottom sheet, preview panel suppression, and swimlane header hiding.
Adds mobile-chrome project (Pixel 5) to playwright config.

* fix(ui): fix mobile E2E test failures in CI

Exclude mobile tests from chromium project (wrong viewport), add
startIndex to Embla carousel to fix initial scroll race condition,
fix strict locator for menu heading, use first step for swimlane test.

* fix(ui): fix create task dialog button layout on mobile

Make StartTaskSplitButton full-width on mobile, hide dropdown chevron
on small screens, and show a visible "Create only" button instead.

* fix(ui): match header button sizes and add icon to create-only action

Align hamburger menu button with changelog/health buttons by removing
explicit h-10 w-10 override. Add IconPlus to "Create without starting
agent" in both the desktop dropdown and mobile button.

* fix(ui): address code review feedback for mobile kanban

- Base hideHeaders on workflowFilter/total count, not filtered result
- Clamp mobile column index via useMemo when steps change
- Fix wrong assertion in preview panel test (was checking toBeVisible)
- Separate altDisabled from splitDisabled (no agent needed for create-only)
- Add visible plan mode button on mobile (was hidden behind dropdown)
- Wait for mobile-kanban-layout in page object goto()
- Extract computeBaseDisabled to reduce complexity

* fix(test): fix flaky mobile E2E tests in headless Chrome

- Use instant jump (scrollTo with jump=true) for tab-triggered carousel
  navigation instead of animated scroll that doesn't complete in headless
- Add data-testid to swimlane header to avoid ambiguous Badge locator
  matching column tab buttons
- Add timeout to viewport assertion for resilience

* fix(ui): address review feedback and fix carousel reinitialization

- Stabilize Embla options to prevent carousel reinit on tab change
  (startIndex was causing re-initialization, resetting scroll position)
- Guard programmatic scrolls from triggering select callback revert
- Remove PointerSensor from mobile DnD sensors (conflicts with touch)
- Fix plan mode button using wrong disabled prop on mobile
- Use literal name matching in columnTab locator (avoid regex injection)
- Use toHaveCount(0) for stricter preview panel absence assertion

* fix(ui): use pointerDown gating for carousel swipe sync

Embla's scrollTo doesn't work in headless Chrome, causing the select
event to fire with index 0 and reset the active tab. Fix by only
syncing Embla→tabs on user-initiated pointer interactions (swipes),
not on programmatic scrollTo calls.

Update E2E test to verify tab active state instead of carousel
viewport positions, which are unreliable in headless environments.

* fix(test): add data-testid and data-active to column tabs

Use explicit data attributes for more reliable test targeting
instead of getByRole and CSS class assertions.

* refactor(ui): use touch sensors for tablet and deduplicate getTasksForStep

* fix(ui): improve spacing for stats and settings buttons in mobile menu

apps/web/components/kanban/mobile-menu-sheet.tsx

@@ -153,7 +153,7 @@ function MobileDisplayOptions(props: MobileDisplayOptionsProps) {
 
 function MobileNavLinks({ onOpenChange }: { onOpenChange: (open: boolean) => void }) {
   return (
-    <div className="mt-auto space-y-2">
+    <div className="mt-auto flex flex-col gap-3 pt-4 border-t border-border">
       <Link href="/stats" onClick={() => onOpenChange(false)}>
         <Button variant="outline" className="w-full cursor-pointer">
           <IconChartBar className="h-4 w-4 mr-2" />