fix: make Prompt node editable when connected to LLM node

When a Prompt node receives text from an LLM Generate node, the text
should be editable by the user. Previously, the textarea was marked as
readOnly when there was an incoming text connection, preventing edits
in both the main view and the expanded modal.

Changes:
- Track last received LLM output to detect when it changes
- Only update prompt when LLM node runs again (output changes)
- Allow user edits in between LLM runs
- Remove readOnly restriction on textarea
- Update placeholder text to indicate editability

This allows users to edit the LLM-generated text, which will be
replaced only when the LLM node runs again, not on every render.

Fixes #1470061054246518927

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/components/nodes/PromptNode.tsx

@@ -34,15 +34,23 @@ export function PromptNode({ id, data, selected }: NodeProps<PromptNodeType>) {
     return edges.some((edge) => edge.target === id && edge.targetHandle === "text");
   }, [edges, id]);
 
-  // Get connected text input and update prompt when connection provides text
+  // Track the last received text from connected LLM node to detect when it changes
+  const [lastReceivedText, setLastReceivedText] = useState<string | null>(null);
+
+  // Get connected text input and update prompt when LLM output changes
   useEffect(() => {
     if (hasIncomingTextConnection) {
       const { text } = getConnectedInputs(id);
-      if (text !== null && text !== nodeData.prompt) {
+      // Only update if the incoming text changed (LLM node ran again)
+      if (text !== null && text !== lastReceivedText) {
+        setLastReceivedText(text);
         updateNodeData(id, { prompt: text });
       }
+    } else {
+      // Clear tracking when connection is removed
+      setLastReceivedText(null);
     }
-  }, [hasIncomingTextConnection, id, getConnectedInputs, updateNodeData, nodeData.prompt]);
+  }, [hasIncomingTextConnection, id, getConnectedInputs, updateNodeData, lastReceivedText]);
 
   // Sync from props when not actively editing
   useEffect(() => {
@@ -150,9 +158,8 @@ export function PromptNode({ id, data, selected }: NodeProps<PromptNodeType>) {
             onChange={handleChange}
             onFocus={handleFocus}
             onBlur={handleBlur}
-            placeholder={hasIncomingTextConnection ? "Receiving text from connected node..." : "Describe what to generate..."}
+            placeholder={hasIncomingTextConnection ? "Text from connected node (editable)..." : "Describe what to generate..."}
             className="nodrag nopan nowheel w-full flex-1 min-h-[70px] p-2 text-xs leading-relaxed text-neutral-100 border border-neutral-700 rounded bg-neutral-900/50 resize-none focus:outline-none focus:ring-1 focus:ring-neutral-600 focus:border-neutral-600 placeholder:text-neutral-500"
-            readOnly={hasIncomingTextConnection}
           />
           {nodeData.variableName && (
             <div className="mt-1 text-[10px] text-blue-400 px-2">