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.

src/scene/text/complex_lt.rs

@@ -175,7 +175,7 @@ pub fn apply_along(
                     let insert = offset_pt(insert, fwd, perp, *x, *y);
                     let fwd_angle = fwd[1].atan2(fwd[0]) + rot_deg.to_radians();
                     let resolved = resolve_dxf_special_chars(text);
-                    let text_strokes = lff::tessellate_text_ex(
+                    let (text_strokes, _) = lff::tessellate_text_ex(
                         [insert[0], insert[1]],
                         *tx_scale,
                         fwd_angle,