fix: navbar mobile dropdown clipped left edge - use left-0 instead of right-0

The dropdown was anchored to right-0 of the <details> element.
On mobile, the trigger button sits near the left side of the viewport
so right-0 caused the panel to extend leftward off-screen.
Changing to left-0 opens the panel rightward from the button, keeping
it fully visible.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

frontend/src/components/Navbar.jsx

@@ -139,7 +139,7 @@ export default function Navbar({ minimal = false }) {
                             ☰ {currentItem?.label || 'Izbornik'}
                         </summary>
                         {/* Dropdown je positioniran fixed-like kroz visoki z-index kako ne bi bio odsječen */}
-                        <div className="absolute right-0 top-full mt-1 z-50 min-w-52 rounded-lg border border-border-hairline bg-canvas-elevated shadow-xl">
+                        <div className="absolute left-0 top-full mt-1 z-50 min-w-52 rounded-lg border border-border-hairline bg-canvas-elevated shadow-xl">
                             <div className="border-b border-border-hairline px-3 py-2 text-[11px] uppercase tracking-wide text-text-muted">
                                 Navigacija
                             </div>