feat: improve template and component responsiveness

[pkosiec]

Summary

Audit and improve responsiveness across the AppKit template and appkit-ui components so that scaffolded apps are mobile-friendly out of the box.

What was fixed

Template (affects every databricks apps init app):

• Mobile navigation: Added Sheet/drawer nav with hamburger menu on mobile (<768px), horizontal nav on desktop. Uses useIsMobile hook and Sheet component from appkit-ui.
• Viewport-relative chat heights: Replaced fixed h-[600px] with h-[min(600px,70vh)] on AgentChat, GeniePage, and ServingPage — prevents clipping on short mobile viewports.
• Files page stacking: Directory list + preview panel now stack vertically on mobile (flex-col md:flex-row). Toolbar wraps responsively.
• Jobs page wrapping: Controls use flex-wrap and input uses w-full sm:w-48 so they don't overflow on narrow screens.
• Responsive padding: Header and main content use px-4 sm:px-6 / p-4 sm:p-6.

appkit-ui:

• DataTable pagination: Footer stacks on mobile (flex-col-reverse sm:flex-row) so controls don't squish together.
• Chart label overlap: Added containLabel: true to cartesian chart grid config. This makes ECharts auto-size the grid to include rotated axis labels, preventing them from overlapping the bottom legend.
• Export useIsMobile hook: Now exported from @databricks/appkit-ui/react for consumer use.

Tooling:

• Fix generate-app-templates: Added missing genie.genie-space.name field for genie templates.

What was already responsive (no changes needed)

• Charts (width): echarts-for-react auto-resizes width; height is consumer-configurable via prop.
• Genie components: Well-structured flexbox layout with ScrollArea and ResizeObserver. Message bubbles use max-w-[80%] + break-words.
• File browser components: DirectoryList, FileEntry, FilePreviewPanel already handle overflow and truncation.
• shadcn/ui primitives: Dialog, Sheet, Drawer, Breadcrumb, Pagination, etc. all use Radix viewport-aware positioning and Tailwind responsive classes.

Screenshots

Screenshots taken from the generated appkit-all-in-one template using Chrome DevTools MCP.

Desktop (1440x900)

Home	Analytics	Files	Genie
Horizontal nav	3-column grid, charts	Side-by-side layout	Chat container

Mobile (375x812)

Home	Nav Open	Genie Messages	Files	Serving	Analytics
Hamburger menu	Sheet with vertical links	User/AI bubbles at max-w-80%	Stacked vertically	Viewport-relative height	Single-column cards

Test plan

• pnpm build passes
• pnpm test passes (3 pre-existing telemetry test failures, unrelated)
• pnpm -r typecheck passes
• Generated appkit-all-in-one template with DATABRICKS_CLI=dbx pnpm generate:app-templates
• Installed local SDK tarballs and ran dev server
• Chrome DevTools MCP visual verification at 375px (mobile) and 1440px (desktop)
  • Mobile: hamburger nav with Sheet, viewport-relative heights, stacked Files, Genie message bubbles responsive
  • Desktop: horizontal nav, multi-column grids, side-by-side Files layout, charts with proper label spacing