fix(canvas/mobile): WCAG 2.4.7 focus-visible rings — MobileCanvas reset zoom + MobileComms filter buttons

MobileCanvas: reset zoom button had no focus indicator — added
focus-visible:ring-2 with emerald-500 ring (consistent with other
mobile interactive elements in the same branch).

MobileComms: filter toggle buttons (All / Errors) had no focus indicator
— added focus-visible:ring-2 with emerald-500 ring.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

canvas/src/components/mobile/MobileCanvas.tsx

@@ -223,6 +223,7 @@ export function MobileCanvas({
             textTransform: "uppercase",
             fontWeight: 600,
           }}
+          className="focus:outline-none focus-visible:ring-2 focus-visible:ring-emerald-500 focus-visible:ring-offset-2 focus-visible:ring-offset-zinc-100 dark:focus-visible:ring-offset-zinc-900"
         >
           Reset
         </button>

canvas/src/components/mobile/MobileComms.tsx

@@ -231,6 +231,7 @@ export function MobileComms({ dark }: { dark: boolean }) {
                 fontSize: 13,
                 fontWeight: 500,
               }}
+              className="focus:outline-none focus-visible:ring-2 focus-visible:ring-emerald-500 focus-visible:ring-offset-2 focus-visible:ring-offset-zinc-100 dark:focus-visible:ring-offset-zinc-900"
             >
               {o.label}
               <span