fix: crisis overlay focuses enabled Call 988 link instead of disabled button (closes #69)

The crisis overlay's showOverlay() was calling overlayDismissBtn.focus()
immediately after setting overlayDismissBtn.disabled = true. Disabled
elements cannot receive focus in browsers, so the overlay opened without
a valid keyboard focus target.

Changes:
- Focus the .overlay-call (Call 988 link) on overlay open — it's always
  enabled and the most important action for a user in crisis
- Move overlayDismissBtn.focus() to the countdown completion handler —
  the button focus now fires when it becomes enabled
- All existing tests pass (139 passed)

index.html

@@ -1045,12 +1045,18 @@ Sovereignty and service always.`;
         overlayTimer = null;
         overlayDismissBtn.disabled = false;
         overlayDismissBtn.textContent = 'Continue to chat';
+        overlayDismissBtn.focus();
       } else {
         overlayDismissBtn.textContent = 'Continue to chat (' + countdown + 's)';
       }
     }, 1000);
 
-    overlayDismissBtn.focus();
+    // Focus the Call 988 link — the dismiss button is disabled during countdown
+    // and disabled elements cannot receive focus. #69
+    var overlayCallBtn = crisisOverlay.querySelector('.overlay-call');
+    if (overlayCallBtn) {
+      overlayCallBtn.focus();
+    }
   }
 
   // Register focus trap on document (always listening, gated by class check)