feat(chat): render Media/Files + Group Info drawers inline, not overlaid

Both right-hand panels used absolute inset-y-0 right-0 and floated on
top of the conversation, hiding the messages directly underneath the
panel and looking unlike Discord's actual layout. Restructure:

* MediaFilesDrawer: drop absolute/z-index/shadow chrome, become a
  static flex column (w-[380px] shrink-0) with a left border. Internal
  layout unchanged.
* GroupInfoPanel: same treatment (w-[320px] shrink-0). Dropped the
  backdrop-blur and slide-up animation that only made sense as a modal.
* ConversationPage: wrap the chat content (voice rail, in-call panel,
  messages list, drag-overlay, input form) in a new
  `flex min-w-0 flex-1 flex-col` chat-column, and make that column a
  sibling of the drawers inside a new `flex flex-1 flex-row` row. The
  conversation header + search bar stay full-width above the row.

Result: opening a drawer narrows the chat column instead of covering
it, matching Discord's behaviour. The chat-column wrapper also carries
the `relative` anchor previously held by the outer wrapper so the
drag-and-drop overlay positions correctly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop/src/components/GroupInfoPanel.tsx

@@ -93,7 +93,7 @@ export function GroupInfoPanel({ open, onClose, conversation }: Props) {
     <aside
       role="dialog"
       aria-label={t('app:group.info_title')}
-      className="absolute inset-y-0 right-0 z-20 flex w-[320px] flex-col border-l border-white/5 bg-ink-900/95 shadow-xl backdrop-blur-xl animate-slide-up"
+      className="flex w-[320px] shrink-0 flex-col border-l border-white/5 bg-ink-900/95"
     >
       <header className="flex items-center justify-between border-b border-white/5 px-5 py-4">
         <div>

apps/desktop/src/components/MediaFilesDrawer.tsx

@@ -31,7 +31,7 @@ export function MediaFilesDrawer({ open, index, senderNameFor, onJumpToMessage,
   if (!open) return null;
 
   return (
-    <aside className="absolute inset-y-0 right-0 z-40 flex w-full max-w-[380px] flex-col border-l border-line bg-surface-2 shadow-2xl dark:bg-[#2b2d31]">
+    <aside className="flex w-[380px] shrink-0 flex-col border-l border-line bg-surface-2 dark:bg-[#2b2d31]">
       <header className="flex min-h-[65px] items-center gap-3 border-b border-line px-4">
         <div className="flex h-10 w-10 items-center justify-center rounded-xl bg-accent/10 text-accent">
           <ImageIcon className="h-5 w-5" />