refactor(renderer): select paths by GPU limits

Keep storage fast paths on capable adapters and use packed or texture fallbacks only when device limits require them.\n\nCompact mesh-edge varyings to avoid WebGL shader rejection.

Cargo.toml

@@ -83,6 +83,11 @@ ttf-parser = "0.25"
 cosmic-text = "0.15"
 lyon_tessellation = "1.0.20"
 
+[dev-dependencies]
+# Shader-interface regression tests. This is already present transitively
+# through wgpu; declaring it here lets tests inspect WGSL entry-point budgets.
+naga = { version = "27", features = ["wgsl-in"] }
+
 [target.'cfg(target_os = "windows")'.dependencies]
 # Win32_System_Com    — COM behind "Set as default app"
 #                       (IApplicationAssociationRegistrationUI dialog).