fix(canvas): add role=status + aria-live to remaining loading states

Three loading-state divs were missing the role/aria pattern that
TemplatePalette.tsx and EmptyState.tsx already follow. Screen readers
get no signal that the page is waiting:

- canvas/src/app/page.tsx — full-screen "Loading canvas..." while
  the websocket hydrates. First paint of the entire app.
- canvas/src/components/settings/TokensTab.tsx — "Loading tokens..."
- canvas/src/components/settings/OrgTokensTab.tsx — "Loading keys..."

Add role="status" + aria-live="polite" to the wrapping div so
assistive tech announces the wait and the eventual transition.
Visual rendering unchanged.

canvas/src/app/page.tsx

@@ -54,7 +54,7 @@ export default function Home() {
   if (hydrating) {
     return (
       <div className="fixed inset-0 flex items-center justify-center bg-surface">
-        <div className="flex flex-col items-center gap-3">
+        <div role="status" aria-live="polite" className="flex flex-col items-center gap-3">
           <Spinner size="lg" />
           <span className="text-xs text-ink-soft">Loading canvas...</span>
         </div>

canvas/src/components/settings/OrgTokensTab.tsx

@@ -182,7 +182,7 @@ export function OrgTokensTab() {
 
       {/* Token list */}
       {loading ? (
-        <div className="flex items-center justify-center gap-2 py-6 text-ink-soft text-xs">
+        <div role="status" aria-live="polite" className="flex items-center justify-center gap-2 py-6 text-ink-soft text-xs">
           <Spinner /> Loading keys...
         </div>
       ) : tokens.length === 0 ? (

canvas/src/components/settings/TokensTab.tsx

@@ -129,7 +129,7 @@ export function TokensTab({ workspaceId }: TokensTabProps) {
 
       {/* Token list */}
       {loading ? (
-        <div className="flex items-center justify-center gap-2 py-6 text-ink-soft text-xs">
+        <div role="status" aria-live="polite" className="flex items-center justify-center gap-2 py-6 text-ink-soft text-xs">
           <Spinner /> Loading tokens...
         </div>
       ) : tokens.length === 0 ? (