Mobile view overhaul: bottom nav, card inventory, camera scanner, PWA

Replace the cramped horizontal sidebar with a 5-tab bottom nav (Home,
Inventory, Scan, Custody, More) with an elevated scan button. Convert
the 10-column inventory table to card-based list on mobile with
scrollable filter pills and long-press selection. Add full-screen
camera barcode scanner using html5-qrcode with post-scan action sheet.
Set up PWA with vite-plugin-pwa for add-to-home-screen. Convert modals
to bottom sheets, add pull-to-refresh, safe-area padding, and iOS
input zoom fix.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/tokens.css

@@ -43,6 +43,9 @@
   --r-lg: 14px;
   --r-xl: 20px;
 
+  /* Touch targets */
+  --touch-min: 44px;
+
   /* Shadow — subtle */
   --shadow-sm: 0 1px 2px oklch(20% 0.02 60 / 0.06);
   --shadow-md: 0 2px 8px oklch(20% 0.02 60 / 0.08);