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/entities/tolerance.rs

@@ -206,7 +206,7 @@ fn tessellate_tolerance(tol: &Tolerance) -> Vec<Vec<[f32; 2]>> {
                 let text_w = cell.len() as f32 * char_w;
                 let tx = cell_x + (cw - text_w) * 0.5;
                 // Tessellate text in local frame then transform
-                let local_strokes =
+                let (local_strokes, _) =
                     lff::tessellate_text_ex([0.0, 0.0], h, 0.0, 1.0, 0.0, "txt", cell);
                 for polyline in local_strokes {
                     let transformed: Vec<[f32; 2]> = polyline
@@ -248,6 +248,7 @@ impl TruckConvertible for Tolerance {
                 strokes,
                 origin,
                 color: None,
+                fill_tris: vec![],
             }]),
             snap_pts: vec![(snap_pt, SnapHint::Insertion)],
             tangent_geoms: vec![],