Fix Output Template visibility and default value

- Set default value "{response}" for new tools
- Add minimum height (80px) so it's always visible
- Add stretch factors to layout so Steps expands, Output stays fixed
- Update placeholder text to be more helpful

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

src/cmdforge/gui/pages/tool_builder_page.py

@@ -153,18 +153,20 @@ class ToolBuilderPage(QWidget):
         steps_btns.addStretch()
         steps_layout.addLayout(steps_btns)
 
-        right_layout.addWidget(steps_box)
+        right_layout.addWidget(steps_box, 1)  # Steps box gets stretch priority
 
         # Output group
         output_box = QGroupBox("Output Template")
         output_layout = QVBoxLayout(output_box)
 
         self.output_input = QTextEdit()
-        self.output_input.setPlaceholderText("{response}\n\nUse {variable} to reference step outputs")
-        self.output_input.setMaximumHeight(100)
+        self.output_input.setPlaceholderText("Use {variable} to reference step outputs, e.g. {response}")
+        self.output_input.setPlainText("{response}")  # Default value
+        self.output_input.setMinimumHeight(80)
+        self.output_input.setMaximumHeight(120)
         output_layout.addWidget(self.output_input)
 
-        right_layout.addWidget(output_box)
+        right_layout.addWidget(output_box, 0)  # Output box stays fixed size
 
         splitter.addWidget(right)
         splitter.setSizes([400, 600])