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/message/Message.tsx

@@ -1189,6 +1189,52 @@ export const Message = React.memo(
                               <MessagePinItem room={room} mEvent={mEvent} onClose={closeMenu} />
                             )}
                           </Box>
+                          {(mEvent.status === EventStatus.NOT_SENT ||
+                            mEvent.status === EventStatus.CANCELLED) && (
+                            <>
+                              <Line size="300" />
+                              <Box direction="Column" gap="100" className={css.MessageMenuGroup}>
+                                <MenuItem
+                                  size="300"
+                                  after={<Icon size="100" src={Icons.Send} />}
+                                  radii="300"
+                                  onClick={() => {
+                                    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+                                    (mx as any).resendEvent(mEvent, room);
+                                    closeMenu();
+                                  }}
+                                >
+                                  <Text
+                                    className={css.MessageMenuItemText}
+                                    as="span"
+                                    size="T300"
+                                    truncate
+                                  >
+                                    Retry Send
+                                  </Text>
+                                </MenuItem>
+                                <MenuItem
+                                  size="300"
+                                  after={<Icon size="100" src={Icons.Cross} />}
+                                  radii="300"
+                                  onClick={() => {
+                                    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+                                    (mx as any).cancelPendingEvent(mEvent);
+                                    closeMenu();
+                                  }}
+                                >
+                                  <Text
+                                    className={css.MessageMenuItemText}
+                                    as="span"
+                                    size="T300"
+                                    truncate
+                                  >
+                                    Cancel Message
+                                  </Text>
+                                </MenuItem>
+                              </Box>
+                            </>
+                          )}
                           {((!mEvent.isRedacted() && canDelete) ||
                             mEvent.getSender() !== mx.getUserId()) && (
                             <>