[Zaxaerith]

Summary

This PR fixes #241 where unordered list bullets (•) and ordered list numbers ({number}.) did not scale with the body text font size.

Root Cause

In crates/ui-egui/src/preview.rs, body text in Block::Item uses draw_spans(..., 14.5 * zoom, ...), where individual spans scale via format_of using 14.5 * zoom * points / 11.0. In contrast, list markers were rendered using ui.label(RichText::new(...).color(tokens.muted)) without .size(...), causing egui to fall back to default body text size (14.0 pt) and ignore both custom font sizes and zoom level.

Fix

• Introduced item_marker_size(spans: &[Span], zoom: f32) -> f32 to resolve the effective font size from item spans (matching draw_spans scale calculation: 14.5 * zoom * points / 11.0, or 14.5 * zoom if unspecified).
• Applied .size(marker_size) to the marker RichText in Block::Item while preserving existing color (tokens.muted), nested indentation, RTL layout, and task checkbox behavior.

Verification

• Added regression tests in crates/ui-egui/src/preview.rs:
  • list_marker_size_follows_effective_body_font_size_and_zoom: verifies default size (14.5), larger font sizes (18pt, 24pt), zoom factors (1.5x, 2.0x), and image span handling.
  • list_items_render_with_marker_scaled_for_ordered_and_unordered: tests rendering layout heights under egui for ordered/unordered lists with default vs larger font sizes, zoom scaling, and nested RTL items.
• Ran targeted tests and linters:
  • cargo test -p notecraft-ui-egui --lib preview: passed (20 passed)
  • cargo test -p notecraft-ui-egui --lib: passed (347 passed)
  • cargo fmt --check -p notecraft-ui-egui: clean
  • cargo clippy -p notecraft-ui-egui --all-targets: clean (0 warnings)
  • cargo xtask text: 0 problems
  • cargo xtask i18n-audit: 0 source findings
  • git diff --check: clean

Fixes #241