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_panel.md

@@ -0,0 +1,52 @@
+---
+name: dag_panel
+kind: component
+lang: cpp
+domain: gfx
+version: "1.0.0"
+purity: impure
+signature: "bool dag_panel(std::vector<DagStep>& pipeline)"
+description: "Panel ImGui para editar un pipeline DAG de shaders. Toolbar con Add Node (popup por kind) y Clear. Lista scrollable de pasos con CollapsingHeader coloreado por kind, selector de source para blends, widgets de control (Slider/XY/Color) y botones Move Up/Down/Delete. Devuelve true si la topologia cambio."
+tags: [dag, shader, imgui, pipeline, editor, gfx, component]
+uses_functions:
+  - dag_catalog_cpp_gfx
+uses_types:
+  - dag_types_cpp_gfx
+returns: []
+returns_optional: false
+error_type: "error_go_core"
+imports: [dag_panel, dag_catalog, dag_types, imgui, algorithm, string, vector]
+tested: false
+tests: []
+test_file_path: ""
+file_path: "cpp/functions/gfx/dag_panel.cpp"
+framework: imgui
+params:
+  - name: pipeline
+    desc: "Vector de DagStep modificado in-place. Add/Delete/Move cambian la topologia. Los sliders solo cambian params."
+output: "true si la topologia cambio (add/delete/move/source_id change). false si solo cambiaron valores de params (sliders). El caller usa este flag para decidir si recompilar el shader."
+---
+
+## Estructura del panel
+
+```
+[+ Add Node]  [N/16 nodes]  [Clear]
+─────────────────────────────────────
+▼ #0 plasma [Gen]
+    velocidad  [slider]
+    escala     [slider]
+    [Move Up(disabled)] [Move Down] [Delete]
+
+▶ #1 blend_mix [Blend]
+    ...
+```
+
+## Colores por kind
+
+- Gen: azul (0.25, 0.55, 0.90)
+- Op: violeta (0.65, 0.40, 0.90)
+- Blend: ambar (0.90, 0.65, 0.15)
+
+## Notas
+
+Los IDs de paso se generan con contador estatico `s_next_id`. Unicos dentro de la sesion. Al anadir un Blend, asigna automaticamente el source_id al paso de hace dos (o el primero si el pipeline tiene menos de 2 pasos). Las mutaciones (delete/move) se aplican al final del loop para no invalidar iteradores.