feat: scaffolding dag_engine_ui (issue 0095 step 2)

ImGui app shell:
- main.cpp con fn::run_app(cfg, render), panel Main placeholder.
- CMakeLists.txt + fn_framework + fn_table_viz opt-in.
- app.md frontmatter base.

Capas HTTP/WS/tabs en commits siguientes.

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

CMakeLists.txt

@@ -0,0 +1,14 @@
+add_imgui_app(dag_engine_ui
+    main.cpp
+)
+target_include_directories(dag_engine_ui PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
+
+# fn_table_viz: provides data_table::render(), viz_render, TQL engine, Lua, LLM.
+# Guard keeps the app compilable in builds where vendor/lua is absent.
+if(TARGET fn_table_viz)
+    target_link_libraries(dag_engine_ui PRIVATE fn_table_viz)
+endif()
+
+if(WIN32)
+    set_target_properties(dag_engine_ui PROPERTIES WIN32_EXECUTABLE TRUE)
+endif()

app.md

@@ -0,0 +1,42 @@
+---
+name: dag_engine_ui
+lang: cpp
+domain: tools
+description: "Frontend ImGui para dag_engine. Lista, lanza e inspecciona DAGs con live updates via WS."
+tags: [imgui]
+uses_functions:
+  # Uncomment when using data_table::render() — provided via fn_table_viz:
+  # - data_table_cpp_viz
+  # - viz_render_cpp_viz
+  # - compute_stage_cpp_core
+  # - compute_pipeline_cpp_core
+  # - compute_column_stats_cpp_core
+  # - auto_detect_type_cpp_core
+  # - tql_emit_cpp_core
+  # - tql_apply_cpp_core
+  # - lua_engine_cpp_core
+  # - join_tables_cpp_core
+  # - tql_to_sql_cpp_core
+  # - llm_anthropic_cpp_core
+uses_types: []
+framework: "imgui"
+entry_point: "main.cpp"
+dir_path: "cpp/apps/dag_engine_ui"
+repo_url: "https://gitea.organic-machine.com/dataforge/dag_engine_ui"
+---
+
+# dag_engine_ui
+
+Frontend ImGui para dag_engine. Lista, lanza e inspecciona DAGs con live updates via WS.
+
+## Build
+
+```bash
+cd cpp && cmake --build build --target dag_engine_ui -j
+```
+
+## Run
+
+```bash
+./cpp/build/dag_engine_ui
+```

main.cpp

@@ -0,0 +1,45 @@
+#include <imgui.h>
+#include "app_base.h"
+#include "core/panel_menu.h"
+#include "core/icons_tabler.h"
+#include "core/logger.h"
+// #include "viz/data_table.h"  // uncomment to enable data_table::render() panel
+
+// Toggles de paneles (visibles desde el menu View del menubar canonico)
+static bool g_show_main = true;
+
+static void draw_main() {
+    if (!ImGui::Begin(TI_HOME " Main", &g_show_main)) {
+        ImGui::End();
+        return;
+    }
+    ImGui::TextUnformatted("Hello from dag_engine_ui");
+    ImGui::End();
+}
+
+static void render() {
+    // El framework dibuja menubar (View/Layouts/Settings/About) y un
+    // DockSpaceOverViewport central (auto_dockspace=true por defecto).
+    // Aqui solo se dibujan los paneles propios de la app.
+    if (g_show_main) draw_main();
+
+    // === Data panel (uncomment to enable) ===
+    // static data_table::State data_state;
+    // static std::vector<data_table::TableInput> data_tables; // populate from your source
+    // data_table::render("main_data", data_tables, data_state);
+}
+
+int main(int /*argc*/, char** /*argv*/) {
+    static fn_ui::PanelToggle panels[] = {
+        { "Main", nullptr, &g_show_main },
+    };
+
+    fn::AppConfig cfg;
+    cfg.title       = "dag_engine_ui — Frontend ImGui para dag_engine. Lista, lanza e inspecciona DAGs con live updates via WS.";
+    cfg.about       = { "dag_engine_ui", "0.1.0", "Frontend ImGui para dag_engine. Lista, lanza e inspecciona DAGs con live updates via WS." };
+    cfg.log         = { "dag_engine_ui.log", 1 };
+    cfg.panels      = panels;
+    cfg.panel_count = sizeof(panels) / sizeof(panels[0]);
+
+    return fn::run_app(cfg, render);
+}