feat: iPad split layout for the Capacitor app (#2104)

* fix: open mobile model/agent panels on tablet-width Capacitor shells and keep composer taps from dismissing the keyboard

* feat: add iPadOS-style split layout to the Capacitor app

- classify the Capacitor shell as mobile in device detection so shared
  surfaces (draft starters, panels) stop falling into tablet branches
- add isIPadApp() and useOrientation() helpers
- iPad: persistent full-height sessions sidebar (mobile sessions surface
  inline), Changes/Files in a right sidebar with header shortcut toggles
- animate sidebar open/close like the desktop sidebars and add
  finger-sized drag-resize with persisted widths
- anchor the overflow menu and the usage/metadata popover next to their
  header buttons regardless of open sidebars

* fix: re-anchor metadata popover on layout shifts and untangle sidebar toggle updates

- recompute the iPad metadata popover anchor via a ResizeObserver on its
  wrapper so sidebar toggles/resizes while it is open cannot leave it
  misplaced
- move the portrait right-panel close out of the setIpadSidebarOpen
  updater into plain sequential state updates

packages/ui/src/components/chat/ChatInput.tsx

@@ -556,6 +556,16 @@ const ComposerAttachmentControls = React.memo(function ComposerAttachmentControl
                         type="button"
                         className={footerIconButtonClass}
                         onClick={props.onOpenMobileSheet}
+                        // Same guard as PermissionAutoAcceptButton: keep the tap
+                        // from dismissing the keyboard. On Android's
+                        // resizes-content viewport the keyboard-close relayout
+                        // moves this button mid-tap and the click never lands.
+                        onMouseDown={(event) => event.preventDefault()}
+                        onPointerDownCapture={(event) => {
+                            if (event.pointerType === 'touch') {
+                                event.preventDefault();
+                            }
+                        }}
                         title={t('chat.chatInput.actions.addAttachment')}
                         aria-label={t('chat.chatInput.actions.addAttachment')}
                     >
@@ -4087,7 +4097,12 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
     }, [newSessionDraftOpen, openNewSessionDraft, currentDirectory]);
 
     const openMobileAttachSheet = React.useCallback(() => {
+        // Same order as handleOpenMobilePanel: mark the sheet open BEFORE the
+        // blur so the collapse watcher sees an overlay when the keyboard-close
+        // lands. The trigger button blocks the tap's own focus transfer, so
+        // the keyboard must be dismissed explicitly here.
         setMobileAttachMenuOpen(true);
+        textareaRef.current?.blur();
     }, []);
 
     const mobileComposerExpandedRef = React.useRef(mobileComposerExpanded);