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_helper_bullets.py

@@ -57,3 +57,29 @@ def test_render_passes_numbered_list_intact_to_imgui_md():
   assert "1. First question" in rendered_text
   assert "2. Second question" in rendered_text
   assert not mock_imgui.bullet.called, "no manual imgui.bullet should be added — let imgui_md handle list rendering"
+
+def test_normalize_nested_list_endings_inserts_blank_after_nested_item():
+ r = MarkdownRenderer()
+ text = "- top\n  - nested last\nnext paragraph\n"
+ out = r._normalize_nested_list_endings(text)
+ assert "  - nested last\n\nnext paragraph" in out, f"expected blank line between nested list item and less-indented next line, got {out!r}"
+
+def test_normalize_nested_list_endings_does_not_insert_blank_for_top_level_list():
+ r = MarkdownRenderer()
+ text = "- one\n- two\n- three\nnext paragraph\n"
+ out = r._normalize_nested_list_endings(text)
+ assert out == text, f"top-level list ending should not trigger blank line insertion, got {out!r}"
+
+def test_normalize_nested_list_endings_does_not_double_blank():
+ r = MarkdownRenderer()
+ text = "- a\n  - b\n\nalready blank\n"
+ out = r._normalize_nested_list_endings(text)
+ assert out == text, f"already-blank separator should not get doubled, got {out!r}"
+
+def test_normalize_bullet_delimiters_still_converts_asterisk():
+ r = MarkdownRenderer()
+ text = "- one\n* two\n+ three\n"
+ out = r._normalize_bullet_delimiters(text)
+ assert "- one" in out
+ assert "- two" in out and "* two" not in out, f"* must be converted to -, got {out!r}"
+ assert "+ three" in out, f"+ must be left alone, got {out!r}"