feat(web): remove max-width constraint and reduce main padding

Remove maxWidth: 1400 and margin: 0 auto from AppShell main container.
Reduce padding from 2rem to 1rem so content fills available browser width.
Adjust height calc in ItemsPage and AuditPage from 80px to 64px offset
to account for reduced top padding.

Closes #16

web/src/components/AppShell.tsx

@@ -96,7 +96,7 @@ export function AppShell() {
         )}
       </header>
 
-      <main style={{ maxWidth: 1400, margin: '0 auto', padding: '2rem' }}>
+      <main style={{ padding: '1rem 1rem 0 1rem' }}>
         <Outlet />
       </main>
     </>

web/src/pages/AuditPage.tsx

@@ -47,7 +47,7 @@ export function AuditPage() {
       style={{
         display: "flex",
         flexDirection: "column",
-        height: "calc(100vh - 80px)",
+        height: "calc(100vh - 64px)",
         paddingBottom: 28,
       }}
     >

web/src/pages/ItemsPage.tsx

@@ -170,7 +170,7 @@ export function ItemsPage() {
       style={{
         display: "flex",
         flexDirection: "column",
-        height: "calc(100vh - 80px)",
+        height: "calc(100vh - 64px)",
         paddingBottom: 28,
       }}
     >