feat(fonts): system TrueType support with shaping and fallback

Add a TrueType/OpenType render path alongside the LFF stroke engine so
users can pick fonts installed on their machine for text and MText.

- Discover system families via fontdb (sysfont) and list them in the
  text-style picker.
- Extract glyph outlines with ttf-parser, flattened into wire strokes
  normalized to the same 9-unit cap-height space as LFF glyphs.
- Shape runs with cosmic-text (ligatures, Arabic joining, kerning, bidi)
  plus automatic font fallback: a glyph missing from the chosen family
  is taken from another installed font.
- Unify both sources behind a single Face type; a shared run tokenizer
  drives the stroke (per-glyph) and shaped (TTF) renderers identically.
- Stroke fonts now fall back to a system TTF (cosmic-text picks it) for
  characters no LFF font covers, replacing the unicode/iso3098 chain.

Also trim the embedded LFF set from 47 to 26, keeping the AutoCAD-SHX
equivalents and dropping LibreCAD-only fonts now covered by TrueType.

LFF builtins keep priority over same-named system fonts so DXF text
renders identically across machines.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

Cargo.lock

@@ -18,7 +18,9 @@ version = "0.5.7"
 dependencies = [
  "acadrust",
  "bytemuck",
+ "cosmic-text",
  "flate2",
+ "fontdb",
  "glam 0.33.0",
  "iced",
  "image",
@@ -34,6 +36,7 @@ dependencies = [
  "truck-modeling",
  "truck-polymesh",
  "truck-shapeops",
+ "ttf-parser",
  "ureq",
  "windows-sys 0.61.2",
  "winresource",