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/attribute.rs

@@ -278,7 +278,7 @@ fn build_attr_truck(input: AttrTextInputs<'_>, document: &acadrust::CadDocument)
             anchor_f64[0] - (anchor_local_x as f64 * cos_r - local_y_for_line as f64 * sin_r),
             anchor_f64[1] - (anchor_local_x as f64 * sin_r + local_y_for_line as f64 * cos_r),
         ];
-        let strokes = lff::tessellate_text_ex(
+        let (strokes, fill_tris) = lff::tessellate_text_ex(
             [0.0, 0.0],
             input.height as f32,
             rotation,
@@ -291,6 +291,7 @@ fn build_attr_truck(input: AttrTextInputs<'_>, document: &acadrust::CadDocument)
             strokes,
             origin,
             color: None,
+            fill_tris,
         });
     }
     let _ = input.line_count; // round-trip only — recomputed above