fix(canvas): WCAG 1.1.1 + 2.4.7 scattered accessibility fixes

- ActivityTab: aria-hidden on decorative chevron (▼/▶) and arrow (→) — WCAG 1.1.1
- MemoryTab: aria-hidden on decorative chevron in memory row — WCAG 1.1.1
- WorkspaceNode: aria-hidden on decorative ↻ restart icon — WCAG 1.1.1
- MobileMe: focus-visible:ring-2 on segmented row buttons — WCAG 2.4.7

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

canvas/src/components/WorkspaceNode.tsx

@@ -323,7 +323,7 @@ export function WorkspaceNode({ id, data }: NodeProps<Node<WorkspaceNodeData>>)
             }}
             className="flex items-center gap-1.5 mt-1 w-full bg-accent/10 px-2 py-1 rounded-md border border-accent/40 hover:bg-accent/20 transition-colors text-left focus-visible:ring-2 focus-visible:ring-accent/70 focus-visible:outline-none"
           >
-            <span className="text-[10px] text-accent">↻</span>
+            <span aria-hidden="true" className="text-[10px] text-accent">↻</span>
             <span className="text-[10px] text-accent">Restart to apply changes</span>
           </button>
         )}

canvas/src/components/mobile/MobileMe.tsx

@@ -184,6 +184,7 @@ function SegmentedRow({
               fontSize: 13,
               fontWeight: 600,
             }}
+            className="focus:outline-none focus-visible:ring-2 focus-visible:ring-accent focus-visible:ring-offset-1"
           >
             {o.label}
           </button>

canvas/src/components/tabs/ActivityTab.tsx

@@ -274,7 +274,7 @@ function ActivityRow({
             {formatTime(entry.created_at)}
           </span>
 
-          <span className="text-[9px] text-ink-mid">
+          <span aria-hidden="true" className="text-[9px] text-ink-mid">
             {expanded ? "▼" : "▶"}
           </span>
         </div>
@@ -296,7 +296,7 @@ function ActivityRow({
                 {resolveName(entry.source_id)}
               </span>
             )}
-            <span className="text-[9px] text-ink-mid">→</span>
+            <span aria-hidden="true" className="text-[9px] text-ink-mid">→</span>
             {entry.target_id && (
               <span className="text-[9px] text-accent/80 truncate max-w-[140px]" title={entry.target_id}>
                 {resolveName(entry.target_id)}

canvas/src/components/tabs/MemoryTab.tsx

@@ -368,7 +368,7 @@ export function MemoryTab({ workspaceId }: Props) {
                           TTL {new Date(entry.expires_at).toLocaleString()}
                         </span>
                       )}
-                      <span className="text-[10px] text-ink-mid">
+                      <span aria-hidden="true" className="text-[10px] text-ink-mid">
                         {expanded === entry.key ? "▼" : "▶"}
                       </span>
                     </div>