fix(text): render TTF glyphs as solid fills, fix font fallback, correct Z-order

Text elements previously rendered as hollow wireframe outlines and sometimes
fell back to the wrong system font due to case-sensitive exact matching. Also,
the viewport background grid drew on top of solid entities.

Case-insensitive and partial-name fallback matching (e.g., mapping "arialn"
to "Arial Narrow") is now added to `sysfont::canonical_family_name`, ensuring
text resolves to the correct installed system font.

TrueType font contours are now triangulated into solid fills (`fill_tris`)
using `lyon_tessellation` in `ttf_glyph.rs`. To prevent the GPU from misclassifying
this 2D text as a 3D mesh (which broke flat shading), text tessellation splits
the output into separate outline and fill `WireModel`s.

The background grid is extracted from `SelectionCanvas` into `GridCanvas` and
moved beneath the 3D viewport to ensure proper layering. Finally, `DepthBiasState`
is enabled on all face/fill pipelines to apply a polygon offset, perfectly
resolving Z-fighting between coplanar wireframe lines and solid faces.

Cargo.toml

@@ -65,6 +65,7 @@ ttf-parser = "0.25"
 # obtain positioned (font, glyph-id) runs; outlines come from ttf-parser and
 # render through our own wire pipeline.
 cosmic-text = "0.15"
+lyon_tessellation = "1.0.20"
 
 [target.'cfg(target_os = "windows")'.dependencies]
 # Win32_System_Com    — COM behind "Set as default app"