feat(shaders_lab): DAG pipeline mode with node catalog

- cpp/functions/gfx/dag_types: DagStep, DagNodeDef, DagControl (header-only)
- cpp/functions/gfx/dag_catalog: 10 hardcoded nodes (4 gen, 3 op, 3 blend) ported from shader-dag-blends.jsx
- cpp/functions/gfx/dag_compile: pipeline → GLSL 330 core with fan-in via source_id
- cpp/functions/gfx/dag_uniforms: upload u_params[16] via glUniform4fv
- cpp/functions/gfx/dag_panel: ImGui pipeline editor (add/remove/reorder/controls)
- main.cpp: Code/DAG mode toggle, per-mode compile path and uniforms
- gl_loader: +glUniform4fv
- rebuild Windows .exe

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cpp/functions/gfx/dag_uniforms.md

@@ -0,0 +1,33 @@
+---
+name: dag_uniforms
+kind: function
+lang: cpp
+domain: gfx
+version: "1.0.0"
+purity: impure
+signature: "void dag_uniforms_apply(const std::vector<DagStep>& pipeline, unsigned int program)"
+description: "Sube los params del pipeline al shader activo via glUniform4fv. Construye un float[64] con los params de cada DagStep (hasta 16 pasos) y llama glUniform4fv(u_params, 16, data)."
+tags: [dag, shader, uniforms, opengl, gfx, pipeline]
+uses_functions:
+  - gl_loader_cpp_gfx
+uses_types:
+  - dag_types_cpp_gfx
+returns: []
+returns_optional: false
+error_type: "error_go_core"
+imports: [dag_uniforms, gl_loader, dag_types, vector, algorithm, cstring]
+tested: false
+tests: []
+test_file_path: ""
+file_path: "cpp/functions/gfx/dag_uniforms.cpp"
+params:
+  - name: pipeline
+    desc: "Vector de DagStep. params[0..3] de cada step se copian en data[i*4..i*4+3]. Steps mas alla de MAX_NODES=16 se ignoran."
+  - name: program
+    desc: "ID del programa GL activo. Debe haber sido activado con glUseProgram antes de llamar."
+output: "Efecto lateral: actualiza el uniform u_params[16] en el programa GL activo para el frame actual."
+---
+
+## Notas
+
+El array data[64] se inicializa a 0 antes de copiar, por lo que steps no usados quedan en cero. El caller es responsable de activar el programa antes de llamar.