Shaders draw in the sprite's own pass: a Mesh with the graph's fragment, no filter (#77)

A sprite's picture is now a Mesh (unit quad, sibling of its Graphics node, which keeps
only the hit area); a worn shader replaces Pixi's fragment in that draw, so there is no
intermediate texture and no extra render pass. Measured on the HD 630: 400 shaded
sprites hold 60 fps (was 34), 800 hold 56 (was 20).

Two Pixi facts the code leans on: a mesh's texture is bound only for Pixi's own shader,
so GraphShader.wear hands it over; and MeshPipe caches whether a mesh batches and
re-checks it only in a frame without structure changes, so switching a shader on or
off calls mesh.unload().

The console panel mirrors console.group/groupCollapsed/groupEnd and fills the %s %d
%o %c directives, so Pixi's deprecation warning shows its head, not only its stack.
E2E 12 guards against the addChild-on-Graphics warning, 28 counts shaders instead of
filters.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tests/core/shaders.test.ts

@@ -203,6 +203,8 @@ describe('compileShader', () => {
     const { fragment } = compiled;
     for (const name of ['brightness', 'contrast', 'saturation'])
       expect(fragment).toContain(`uniform float u_${name};`);
+    // Drawn in the sprite's own pass: the tint goes in before the graph, premultiplied like the texel.
+    expect(fragment).toContain('vec4 texel = texture(uTexture, vTextureCoord) * vColor;');
     expect(fragment).toContain('vec3 rgb = texel.a > 0.0 ? texel.rgb / texel.a : texel.rgb;');
     expect(fragment).toMatch(/float n\d+_result = \(n\d+_value - 1\.0\);/);
     expect(fragment).toMatch(/vec3 n\d+_result = \(n\d+_color \+ vec3\(n\d+_result\)\);/);