fix(gui): add resizable splitter between Files and Screenshots panels

Added:
- _files_split_v state (0.5 default) for split ratio
- _files_open and _shots_open tracking for collapse state
- Splitter bar between collapsing headers when both open
- Splitter updates _files_split_v based on mouse drag

src/gui_2.py

@@ -873,11 +873,25 @@ class App:
     exp, opened = imgui.begin("Files & Media", self.show_windows["Files & Media"])
     self.show_windows["Files & Media"] = bool(opened)
     if exp:
-     if imgui.collapsing_header("Files"):
+     if not hasattr(self, "_files_split_v"): self._files_split_v = 0.5
+     if not hasattr(self, "_files_open"): self._files_open = True
+     if not hasattr(self, "_shots_open"): self._shots_open = True
+     if imgui.collapsing_header("Files", imgui.TreeNodeFlags_.default_open if self._files_open else 0):
+      self._files_open = True
       self._render_files_panel()
-     if imgui.collapsing_header("Screenshots"):
+     else:
+      self._files_open = False
+     if self._files_open and self._shots_open:
+      imgui.button("###files_media_splitter", imgui.ImVec2(-1, 4))
+      if imgui.is_item_active():
+       avail = imgui.get_content_region_avail().y
+       if avail > 0: self._files_split_v = max(0.2, min(0.8, self._files_split_v + imgui.get_io().mouse_delta.y / avail))
+     if imgui.collapsing_header("Screenshots", imgui.TreeNodeFlags_.default_open if self._shots_open else 0):
+      self._shots_open = True
       self._render_screenshots_panel()
-    imgui.end()
+     else:
+      self._shots_open = False
+     imgui.end()
    if self.show_windows.get("AI Settings", False):
     exp, opened = imgui.begin("AI Settings", self.show_windows["AI Settings"])
     self.show_windows["AI Settings"] = bool(opened)