fix(gui): restore while clipper.step() loop in render_prior_session_view

ROOT CAUSE: During a previous indentation fix, the 'while clipper.step():'
line was accidentally removed from render_prior_session_view. Without
the step() loop, the ListClipper's display_start/display_end stay at
their initial values (0/0 or similar), so NO discussion entries
were rendered even though 233 entries were present in
app.prior_disc_entries. The user saw only a single entry because the
list clipper was never advanced.

FIX: Restore the 'while clipper.step():' line. Re-indent the entire
prior_scroll block to consistent 1-space (function), 2-space (inside
style_color), 3-space (inside child + while), 4-space (inside for)
indentation. Now all 233 entries will render through the list clipper.

Tests:
- 28/28 broad regression pass

src/gui_2.py

@@ -3590,7 +3590,8 @@ def render_prior_session_view(app: App) -> None:
   imgui.separator()
   avail = imgui.get_content_region_avail()
   with imscope.child("prior_scroll", imgui.ImVec2(avail.x, avail.y), imgui.WindowFlags_.horizontal_scrollbar):
-    clipper = imgui.ListClipper(); clipper.begin(len(app.prior_disc_entries))
+   clipper = imgui.ListClipper(); clipper.begin(len(app.prior_disc_entries))
+   while clipper.step():
     for idx in range(clipper.display_start, clipper.display_end):
      entry = app.prior_disc_entries[idx];
      with imscope.id(f"prior_disc_{idx}"):
@@ -3608,7 +3609,6 @@ def render_prior_session_view(app: App) -> None:
        with theme.ai_text_style():
         markdown_helper.render(content, context_id=f'prior_disc_{idx}')
       imgui.separator()
-
 def render_thinking_indicator(app: App) -> None:
  is_thinking = app.ai_status in ['sending...', 'streaming...', 'running powershell...']
  if is_thinking: