ux: reply null state, location error feedback, retry send, reaction keyboard nav

- Reply: distinguish loading (placeholder) from not-found (null) — show
  "Original message not available" instead of a stuck loading bar
- RoomInput: geolocation errors now surface inline (denied / timed out /
  unsupported); location button shows Spinner during fetch and is disabled
- Message menu: Retry Send + Cancel Message items appear when a message
  is in NOT_SENT or CANCELLED state, calling mx.resendEvent / cancelPendingEvent
- ReactionViewer: sidebar gains role=listbox / role=option and ArrowUp/Down
  keyboard navigation between reactions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/features/room/RoomInput.tsx

@@ -24,6 +24,7 @@ import {
   OverlayCenter,
   PopOut,
   Scroll,
+  Spinner,
   Text,
   config,
   toRem,
@@ -183,8 +184,13 @@ export const RoomInput = forwardRef<HTMLDivElement, RoomInputProps>(
 
     const [toolbar, setToolbar] = useSetting(settingsAtom, 'editorToolbar');
     const [locating, setLocating] = React.useState(false);
+    const [locationError, setLocationError] = React.useState<string | null>(null);
     const handleShareLocation = () => {
-      if (!navigator.geolocation) return;
+      if (!navigator.geolocation) {
+        setLocationError('Geolocation not supported.');
+        setTimeout(() => setLocationError(null), 4000);
+        return;
+      }
       setLocating(true);
       navigator.geolocation.getCurrentPosition(
         (pos) => {
@@ -197,7 +203,17 @@ export const RoomInput = forwardRef<HTMLDivElement, RoomInputProps>(
             geo_uri: geoUri,
           } as any);
         },
-        () => setLocating(false),
+        (err) => {
+          setLocating(false);
+          const msg =
+            err.code === 1
+              ? 'Location access denied.'
+              : err.code === 3
+                ? 'Location timed out.'
+                : 'Failed to get location.';
+          setLocationError(msg);
+          setTimeout(() => setLocationError(null), 4000);
+        },
         { timeout: 10000 },
       );
     };
@@ -858,8 +874,22 @@ export const RoomInput = forwardRef<HTMLDivElement, RoomInputProps>(
                   {gifError}
                 </Text>
               )}
+              {locationError && (
+                <Text
+                  size="T200"
+                  style={{
+                    color: 'var(--tc-danger-normal)',
+                    padding: '2px 6px',
+                    alignSelf: 'center',
+                    whiteSpace: 'nowrap',
+                  }}
+                >
+                  {locationError}
+                </Text>
+              )}
               <IconButton
                 onClick={handleShareLocation}
+                disabled={locating}
                 aria-label="Share location"
                 variant="SurfaceVariant"
                 size="300"
@@ -867,17 +897,7 @@ export const RoomInput = forwardRef<HTMLDivElement, RoomInputProps>(
                 title="Share location"
               >
                 {locating ? (
-                  <Text
-                    size="T200"
-                    style={{
-                      fontWeight: 800,
-                      fontSize: '10px',
-                      letterSpacing: '0.04em',
-                      lineHeight: 1,
-                    }}
-                  >
-                    ...
-                  </Text>
+                  <Spinner variant="Secondary" size="100" />
                 ) : (
                   <Icon src={Icons.SpaceGlobe} size="100" />
                 )}