#184 AF-290 fix(ui): collapse the top nav into a drawer on mobile and tablet screens

[Anonymous]

Originally created by: ddlaurin

Closes [#154]

Problem

The header is a single flex row whose children default to min-width: auto, so
nothing could shrink below its content width. Platform view needs ~1079px to lay
its seven tabs out inline, so a 375px viewport forced the document to 962px and
the whole page scrolled sideways.

Change

• Tabs collapse into a Sheet drawer below lg (1024px), covering phones and tablets
• Header spacing tightens between lg and xl so all seven tabs fit at 1024px
• Drawer open state is derived from the current route, so back/forward, the org
  switcher and programmatic navigation all close it
• Brand wordmark and the "Hire agent" label collapse below sm

Checks

• pnpm exec tsc --noEmit clean
• pnpm lint clean
• pnpm exec playwright test 251 passed (including 8 new specs)

[Anonymous]

Originally posted by: AnaniyaT

isActive prefix-matches, so Overview counts as active on every platform page. It was already like that inline, but the drawer's background fill makes both rows look selected. An exact match for the overview route would fix it, like Home does in org view.