Give the terminal and Add Project buttons a reason a screen reader can hear

Both were the defect the new hook exists for. The sidebar's Claude terminal
button is disabled whenever the container is not running and never said so —
its `title` names the action, so the precondition appeared nowhere in the
accessibility tree at all. Add Project's submit button is disabled while an
add is in flight, and its only signal is the label swapping to "Adding…" on
an element a screen reader can no longer reach.

The submit button needs a second guard the hook cannot supply: Enter inside
a text field submits a form without touching the submit button, so
`handleSubmit` now returns early while loading. Without it, swapping
`disabled` for `aria-disabled` would have turned an accessibility fix into a
double-submit bug.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011YPqHpjV4EL6RNEwrRKqQm

app/src/components/projects/AddProjectDialog.tsx

@@ -55,6 +55,10 @@ export default function AddProjectDialog({ onClose }: Props) {
 
   const handleSubmit = async (e?: React.FormEvent) => {
     if (e) e.preventDefault();
+    // The submit button is `aria-disabled` rather than `disabled` while an add
+    // is in flight, and Enter inside a text field submits the form without
+    // touching the button at all. Both routes end here, so the guard does too.
+    if (loading) return;
     if (!name.trim()) {
       setError("Project name is required");
       return;
@@ -97,7 +101,19 @@ export default function AddProjectDialog({ onClose }: Props) {
           <Button size="md" variant="ghost" onClick={onClose}>
             Cancel
           </Button>
-          <Button size="md" variant="primary" type="submit" form={formId} disabled={loading}>
+          <Button
+            size="md"
+            variant="primary"
+            type="submit"
+            form={formId}
+            unavailable={loading}
+            unavailableReason="The project is being added. Wait for it to finish."
+            title={
+              loading
+                ? "The project is being added. Wait for it to finish."
+                : undefined
+            }
+          >
             {loading ? "Adding…" : "Add Project"}
           </Button>
         </>