fix(canvas/chat): WCAG 2.4.7 focus-visible on AgentCommsPanel + AttachmentViews

- AgentCommsPanel: add focus-visible ring + aria-label to Retry button
  (error state). Add focus-visible to CommsTab tab buttons.
- AttachmentViews: add focus-visible ring + aria-label to Remove button
  (PendingAttachmentPill) and Download button (AttachmentChip).

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

canvas/src/components/tabs/chat/AgentCommsPanel.tsx

@@ -405,7 +405,7 @@ export function AgentCommsPanel({ workspaceId }: { workspaceId: string }) {
         </p>
         <button
           onClick={loadInitial}
-          className="text-[10px] px-2 py-0.5 rounded bg-red-800/40 text-bad hover:bg-red-700/50 transition-colors"
+          className="text-[10px] px-2 py-0.5 rounded bg-red-800/40 text-bad hover:bg-red-700/50 transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-red-500/60 focus-visible:ring-offset-1"
         >
           Retry
         </button>
@@ -610,7 +610,7 @@ function PeerTabButton({
       aria-selected={active}
       tabIndex={active ? 0 : -1}
       onClick={onClick}
-      className={`shrink-0 px-3 py-1.5 text-[10px] font-medium transition-colors whitespace-nowrap ${
+      className={`shrink-0 px-3 py-1.5 text-[10px] font-medium transition-colors whitespace-nowrap focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-cyan-500/60 focus-visible:ring-offset-1 ${
         active
           ? "border-b-2 border-cyan-500 text-cyan-200"
           : "border-b-2 border-transparent text-ink-mid hover:text-ink-mid"

canvas/src/components/tabs/chat/AttachmentViews.tsx

@@ -33,7 +33,7 @@ export function PendingAttachmentPill({
       <button
         onClick={onRemove}
         aria-label={`Remove ${file.name}`}
-        className="ml-0.5 text-ink-mid hover:text-ink transition-colors shrink-0"
+        className="ml-0.5 text-ink-mid hover:text-ink transition-colors shrink-0 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-accent/60 focus-visible:ring-offset-1"
       >
         <svg width="10" height="10" viewBox="0 0 16 16" fill="none" aria-hidden="true">
           <path d="M4 4l8 8M12 4l-8 8" stroke="currentColor" strokeWidth="1.6" strokeLinecap="round" />
@@ -62,8 +62,9 @@ export function AttachmentChip({
   return (
     <button
       onClick={() => onDownload(attachment)}
+      aria-label={`Download ${attachment.name}`}
       title={`Download ${attachment.name}`}
-      className={`flex items-center gap-1.5 rounded-md border px-2 py-1 text-[10px] transition-colors max-w-full ${toneClasses}`}
+      className={`flex items-center gap-1.5 rounded-md border px-2 py-1 text-[10px] transition-colors max-w-full focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-accent/60 focus-visible:ring-offset-1 ${toneClasses}`}
     >
       <FileGlyph className="shrink-0 opacity-70" />
       <span className="truncate">{attachment.name}</span>