fix(markdown): strip backticks in table cells + add nested-list overlap workaround

FIX 1 (src/markdown_table.py): Cells now use imgui_md.render(c) instead of
imgui.text_wrapped(c). imgui_md uses MD4C which strips backtick-delimited
inline code spans BEFORE rendering, so backticks no longer appear as
literal characters in cell content. Side benefit: inline emphasis
(*foo*, **bar**) now renders in cells too.

FIX 2 (src/markdown_helper.py): Added MarkdownRenderer._normalize_nested_list_endings.
Upstream imgui_md (mekhontsev/imgui_md) BLOCK_UL exit only calls
ImGui::NewLine() for top-level list endings. For nested list endings, no
NewLine is emitted, so the next text starts at the same Y as the last
list item, causing visual overlap. The preprocessor inserts a blank
line before any line that follows a list item with MORE indent than
itself, forcing a paragraph break. Cannot fix the C++ from Python.

Tests:
- test_markdown_table_wrapped.py: updated to assert imgui_md.render is
  called for cell content (not imgui.text_wrapped).
- test_markdown_helper_bullets.py: added 4 tests for the new preprocessors
  (nested-list blank insertion + bullet delimiter conversion + edge cases).

20/20 markdown unit tests pass. 1-space indentation throughout.

KNOWN LIMITATIONS (cannot fix without forking imgui_md C++):
- Inline code spans render as plain text (no monospace font in cells)
- The ' * ' bullet delimiter has a Y-overlap bug upstream
  (workaround: pre-convert to '- ' via _normalize_bullet_delimiters)
- Nested list ending overlap (workaround: insert blank line via
  _normalize_nested_list_endings)

tests/test_markdown_table_wrapped.py

@@ -12,32 +12,44 @@ def _setup_mocks(mock_imgui):
  mock_imgui.text = MagicMock()
  mock_imgui.end_table = MagicMock()
 
-def test_render_table_uses_text_wrapped_for_cells():
+def _setup_md_mocks():
+ from src.markdown_table import imgui_md as md_mod
+ md_mod.render = MagicMock()
+
+def test_render_table_routes_cell_content_through_imgui_md():
  block = TableBlock(headers=["A"], rows=[["hello"]], span=(0, 2))
- with patch("src.markdown_table.imgui") as mock_imgui:
+ with patch("src.markdown_table.imgui") as mock_imgui, \
+      patch("src.markdown_table.imgui_md") as mock_md:
   _setup_mocks(mock_imgui)
+  _setup_md_mocks()
   render_table(block)
-  mock_imgui.text_wrapped.assert_any_call("hello")
+  mock_md.render.assert_any_call("hello"), "cell content must be routed through imgui_md.render (so MD4C strips backticks and handles inline emphasis)"
 
 def test_render_table_uses_table_headers_row_for_headers():
  block = TableBlock(headers=["A"], rows=[["hello"]], span=(0, 2))
- with patch("src.markdown_table.imgui") as mock_imgui:
+ with patch("src.markdown_table.imgui") as mock_imgui, \
+      patch("src.markdown_table.imgui_md") as mock_md:
   _setup_mocks(mock_imgui)
+  _setup_md_mocks()
   render_table(block)
   assert mock_imgui.table_headers_row.called, "table_headers_row must be called exactly once to render the header row"
   assert mock_imgui.table_headers_row.call_count == 1, f"table_headers_row must be called exactly once (not {mock_imgui.table_headers_row.call_count} — would cause double-header bug)"
 
 def test_render_table_does_not_use_text_for_cells():
  block = TableBlock(headers=["A"], rows=[["hello"]], span=(0, 2))
- with patch("src.markdown_table.imgui") as mock_imgui:
+ with patch("src.markdown_table.imgui") as mock_imgui, \
+      patch("src.markdown_table.imgui_md") as mock_md:
   _setup_mocks(mock_imgui)
+  _setup_md_mocks()
   render_table(block)
   assert not mock_imgui.text.called, "imgui.text should not be called for table cells"
 
 def test_render_table_uses_width_stretch_for_columns():
  block = TableBlock(headers=["A", "B"], rows=[["1", "2"]], span=(0, 3))
- with patch("src.markdown_table.imgui") as mock_imgui:
+ with patch("src.markdown_table.imgui") as mock_imgui, \
+      patch("src.markdown_table.imgui_md") as mock_md:
   _setup_mocks(mock_imgui)
+  _setup_md_mocks()
   render_table(block)
   assert mock_imgui.table_setup_column.call_count == 2
   for call in mock_imgui.table_setup_column.call_args_list:
@@ -48,10 +60,12 @@ def imgui_flags_passed(args) -> bool:
  if len(args) < 2: return False
  return bool(args[1] & 8)
 
-def test_render_table_text_wrapped_count_matches_cell_count():
+def test_render_table_routes_every_cell_through_imgui_md():
  block = TableBlock(headers=["A", "B"], rows=[["1", "2"], ["3", "4"], ["5", "6"]], span=(0, 5))
- with patch("src.markdown_table.imgui") as mock_imgui:
+ with patch("src.markdown_table.imgui") as mock_imgui, \
+      patch("src.markdown_table.imgui_md") as mock_md:
   _setup_mocks(mock_imgui)
+  _setup_md_mocks()
   render_table(block)
   cell_count = 6
-  assert mock_imgui.text_wrapped.call_count == cell_count, f"text_wrapped must be called exactly {cell_count} times (cells only, not headers), got {mock_imgui.text_wrapped.call_count}"
+  assert mock_md.render.call_count == cell_count, f"imgui_md.render must be called exactly {cell_count} times (one per cell, not headers), got {mock_md.render.call_count}"