feat(mobile): autocomplete redesign for touch surfaces

Command, file/agent, skill, and snippet autocompletes now stop at the top
of the chat area (Capacitor) or the visible viewport edge (mobile
browsers, which pan the page for the keyboard) and may grow that far,
measured live across keyboard settles and viewport changes. On mobile the
keyboard-hint footer and description lines are gone, rows center their
icons, and list overscroll no longer bounces the page behind. Selecting a
command no longer dismisses the keyboard (its rows now block the tap's
focus steal like the composer buttons), and the dead dismissKeyboard
option is removed.

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

@@ -2365,9 +2365,7 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
         }
     }, [inputMode, getCurrentInputSnapshot, currentSessionId, sessionPhase, autoReviewRunning, followUpBehavior, handleQueueMessage]);
 
-    // Draft welcome presets: populate the composer and submit immediately.
-    // getCurrentInputSnapshot reads textareaRef.current.value first, so setting it
-    // synchronously lets handleSubmit pick up the preset text in the same tick.
+    // Draft welcome presets: submit immediately.
     const submitPresetPrompt = React.useCallback((text: string) => {
         // The text goes straight into the submit (see SubmitOptions.presetText)
         // instead of through the composer input — the collapsed mobile pill has
@@ -2393,13 +2391,11 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
     }, []);
 
     const handleDictationInsertAndSend = React.useCallback((text: string) => {
-        const textarea = textareaRef.current;
-        const next = appendInlineText(textarea?.value ?? messageRef.current, text);
-        if (textarea) {
-            textarea.value = next;
-        }
-        setMessage(next);
-        void handleSubmitRef.current();
+        // Same as preset chips: the composed text goes into the submit as an
+        // explicit override instead of being staged in the textarea, which may
+        // not be mounted (collapsed mobile pill).
+        const next = appendInlineText(textareaRef.current?.value ?? messageRef.current, text);
+        void handleSubmitRef.current({ presetText: next });
     }, []);
 
     // Preset chips rendered outside this component (e.g. under the welcome