feat(mobile): chat input keybinds + safe-area + tap targets + overflow safety

- ChatInput: e.nativeEvent.isComposing early-return added (CJK IME
  safety — first Enter of a composition no longer submits). Bare-Enter
  send path gated by !isMobile so mobile inserts a newline; send is
  button-only. Cmd/Ctrl+Enter and Shift+Cmd/Ctrl+Enter retained as
  desktop secondary bindings. Placeholder is now viewport-aware. Outer
  wrapper gets paddingBottom: env(safe-area-inset-bottom) so iOS home
  indicator doesn't overlap.
- MessageBubble: ActionRow buttons (Copy / Regenerate / Fork / Trash)
  bumped to max-md min-h/min-w 44px; opacity-100 on mobile so actions
  don't hide behind a hover-to-reveal pattern. User bubble and
  assistant content wrapper gain break-words + min-w-0 so long
  unbreakable strings (URLs / paths) wrap rather than blowing out
  the column on narrow viewports.
- ChatPane: queued-message dropdown + close X + Stop-generating button
  hit max-md 44px sizing.
- ChatTabBar: per-tab X, +/History/Close-pane action buttons hit
  max-md 44px. Tab close X is force-visible on mobile (no
  hover-to-reveal).
- M8: CodeBlock / Markdown tables / ToolCallCard already wrap
  overflow-x-auto pre-existing — no source change needed there; the
  break-words + min-w-0 additions above are the new defensive layer.

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

apps/web/src/components/MessageBubble.tsx

@@ -266,11 +266,11 @@ function ActionRow({
 
   return (
     <>
-      <div className="flex gap-1 opacity-0 group-hover:opacity-100 transition-opacity">
+      <div className="flex gap-1 opacity-0 group-hover:opacity-100 transition-opacity max-md:opacity-100">
         <button
           type="button"
           onClick={() => void copy()}
-          className="inline-flex items-center justify-center size-6 rounded text-muted-foreground hover:bg-muted hover:text-foreground"
+          className="inline-flex items-center justify-center size-6 rounded text-muted-foreground hover:bg-muted hover:text-foreground max-md:min-h-[44px] max-md:min-w-[44px]"
           aria-label="Copy message"
           title="Copy"
         >
@@ -281,7 +281,7 @@ function ActionRow({
             type="button"
             onClick={() => void regenerate()}
             disabled={!canRegen || regenerating}
-            className="inline-flex items-center justify-center size-6 rounded text-muted-foreground hover:bg-muted hover:text-foreground disabled:opacity-40 disabled:cursor-not-allowed"
+            className="inline-flex items-center justify-center size-6 rounded text-muted-foreground hover:bg-muted hover:text-foreground disabled:opacity-40 disabled:cursor-not-allowed max-md:min-h-[44px] max-md:min-w-[44px]"
             aria-label="Regenerate message"
             title="Regenerate"
           >
@@ -292,7 +292,7 @@ function ActionRow({
           type="button"
           onClick={() => void fork()}
           disabled={!canFork || forking}
-          className="inline-flex items-center justify-center size-6 rounded text-muted-foreground hover:bg-muted hover:text-foreground disabled:opacity-40 disabled:cursor-not-allowed"
+          className="inline-flex items-center justify-center size-6 rounded text-muted-foreground hover:bg-muted hover:text-foreground disabled:opacity-40 disabled:cursor-not-allowed max-md:min-h-[44px] max-md:min-w-[44px]"
           aria-label="Fork from here"
           title="Fork from here"
         >
@@ -302,7 +302,7 @@ function ActionRow({
           type="button"
           onClick={() => setDeleteOpen(true)}
           disabled={!canDelete}
-          className="inline-flex items-center justify-center size-6 rounded text-muted-foreground hover:bg-muted hover:text-destructive disabled:opacity-40 disabled:cursor-not-allowed"
+          className="inline-flex items-center justify-center size-6 rounded text-muted-foreground hover:bg-muted hover:text-destructive disabled:opacity-40 disabled:cursor-not-allowed max-md:min-h-[44px] max-md:min-w-[44px]"
           aria-label="Delete message"
           title="Delete message"
         >
@@ -476,7 +476,7 @@ export function MessageBubble({ message, sessionChats }: Props) {
   if (message.role === 'user') {
     return (
       <div className="group flex flex-col items-end gap-1">
-        <div className="max-w-[80%] rounded-lg bg-primary text-primary-foreground px-3 py-2 text-sm whitespace-pre-wrap">
+        <div className="max-w-[80%] rounded-lg bg-primary text-primary-foreground px-3 py-2 text-sm whitespace-pre-wrap break-words min-w-0">
           {message.content}
         </div>
         <ActionRow message={message} />
@@ -495,7 +495,7 @@ export function MessageBubble({ message, sessionChats }: Props) {
         <ToolCallCard key={tc.id} toolCall={tc} />
       ))}
       {(hasContent || (!hasToolCalls && isStreaming)) && (
-        <div className="max-w-[90%] text-sm leading-relaxed space-y-2">
+        <div className="max-w-[90%] text-sm leading-relaxed space-y-2 break-words min-w-0">
           {hasContent ? <MarkdownBody content={message.content} /> : null}
           {isStreaming && (
             <span className="inline-block w-1.5 h-3.5 align-baseline bg-muted-foreground/60 animate-pulse" />