docs: fix all broken cross-reference links

docs/TROUBLESHOOTING.md

@@ -57,7 +57,7 @@ vulkaninfo  # verify installation
 
 **Symptom:** Program crashes with a surface lost error during rendering.
 
-**Cause:** Display server restarted or GPU context was reset. The [Surface](concepts/GLOSSARY.md#Surface) is permanently invalidated.
+**Cause:** Display server restarted or GPU context was reset. The [Surface](concepts/GLOSSARY.md#surface) is permanently invalidated.
 
 **Fix:** In the tutorial, this means the window needs to be reopened. In production code, handle the `Lost` variant of `CurrentSurfaceTexture` by recreating the surface via `Instance::create_surface()`.
 
@@ -108,7 +108,7 @@ fn exiting(&mut self, event_loop_ctl: &ActiveEventLoop) {
 
 **Symptom:** Triangle renders but is a single uniform color instead of smoothly blending.
 
-**Cause:** Fragment shader returns a constant color instead of passing through `input.vertex_color`. The [rasterizer](concepts/GLOSSARY.md#Rasterizer) interpolates vertex colors automatically, but only if the fragment shader uses them.
+**Cause:** Fragment shader returns a constant color instead of passing through `input.vertex_color`. The [rasterizer](concepts/GLOSSARY.md#rasterizer) interpolates vertex colors automatically, but only if the fragment shader uses them.
 
 **Fix:** Ensure fragment shader returns the interpolated vertex color:
 ```wgsl