phase(N.5) Task 5: mesh_modern.vert + .frag — bindless + SSBO + indirect

New entity shaders for the WB modern rendering path. Modeled on WB's
StaticObjectModern.* but adapted to acdream's lighting model:
- Drops uActiveCells (we cull cells on CPU in WbDrawDispatcher)
- Drops uDrawIDOffset (full passes, no pagination)
- Drops uHighlightColor (deferred to Phase B.4 follow-up; field reserved
  in InstanceData struct comment)
- Preserves mesh_instanced's SceneLighting UBO at binding=1 with 8 lights,
  fog params, lightning flash, per-channel clamp — full visual identity

vert reads InstanceData[] @ binding=0 indexed by gl_BaseInstanceARB +
gl_InstanceID for the per-entity model matrix; reads BatchData[] @
binding=1 indexed by gl_DrawIDARB for the per-group bindless texture
handle + layer.

frag samples sampler2DArray reconstructed from a uvec2 bindless handle
+ uint layer. uRenderPass uniform picks two-pass alpha-test thresholds:
0 = opaque (discard alpha<0.95), 1 = transparent (discard alpha>=0.95
and alpha<0.05).

Not yet wired to the dispatcher — Task 6 sets up shader load + capability
detection in GameWindow; Task 7-10 rewrite the dispatcher to use SSBO +
glMultiDrawElementsIndirect.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/Shaders/mesh_modern.vert

@@ -0,0 +1,53 @@
+#version 430 core
+#extension GL_ARB_bindless_texture : require
+#extension GL_ARB_shader_draw_parameters : require
+
+layout(location = 0) in vec3 aPosition;
+layout(location = 1) in vec3 aNormal;
+layout(location = 2) in vec2 aTexCoord;
+
+struct InstanceData {
+    mat4 transform;
+    // Reserved for Phase B.4 follow-up (selection-blink retail-faithful
+    // highlight): vec4 highlightColor; — extend stride here, increase the
+    // _instanceSsbo upload size in WbDrawDispatcher, add a flat varying out,
+    // and consume in mesh_modern.frag.
+};
+
+struct BatchData {
+    uvec2 textureHandle;   // bindless handle for sampler2DArray
+    uint  textureLayer;    // layer index (always 0 for per-instance composites)
+    uint  flags;           // reserved
+};
+
+layout(std430, binding = 0) readonly buffer InstanceBuffer {
+    InstanceData Instances[];
+};
+
+layout(std430, binding = 1) readonly buffer BatchBuffer {
+    BatchData Batches[];
+};
+
+uniform mat4 uViewProjection;
+
+out vec3 vNormal;
+out vec2 vTexCoord;
+out vec3 vWorldPos;
+out flat uvec2 vTextureHandle;
+out flat uint  vTextureLayer;
+
+void main() {
+    int instanceIndex = gl_BaseInstanceARB + gl_InstanceID;
+    mat4 model = Instances[instanceIndex].transform;
+
+    vec4 worldPos = model * vec4(aPosition, 1.0);
+    gl_Position = uViewProjection * worldPos;
+
+    vWorldPos = worldPos.xyz;
+    vNormal = normalize(mat3(model) * aNormal);
+    vTexCoord = aTexCoord;
+
+    BatchData b = Batches[gl_DrawIDARB];
+    vTextureHandle = b.textureHandle;
+    vTextureLayer = b.textureLayer;
+}