feat: tabs DAG List / Detail / Run Detail via data_table_cpp_viz (issue 0095 step 5)

- tabs.{h,cpp}: 3 paneles que renderizan TableInput con data_table::render() + RowDoubleClick events para drill-down (DAG -> Detail -> Run Detail).
- main.cpp: arranca con auto-fetch DAGs y los 3 tabs visibles por defecto. Panel Main diagnostico apagado.
- CMakeLists.txt: linka empty_state.cpp del registry.
- app.md: uses_functions completo (data_table_cpp_viz + stack TQL + empty_state). Tags: [imgui, dashboard, dag, scheduler, http, websocket].

Funcionalidades:
- DAG List: tabla con Name/Schedule/Last Status/Tags/Valid/File. Status combina last_run (REST) + live_runs (WS). Double-click selecciona DAG.
- DAG Detail: header + Run Now (POST /api/dags/{name}/run) + tabla recent runs. Double-click run abre Run Detail.
- Run Detail: header del run + tabla steps (name/status/exit/duration/started) + CollapsingHeader por step con stdout/stderr.

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

main.cpp

@@ -5,6 +5,7 @@
 #include "core/logger.h"
 #include "data_http.h"
 #include "ws_client.h"
+#include "tabs.h"
 #include "vendor/nlohmann/json.hpp"
 
 #include <string>
@@ -29,8 +30,14 @@ static std::string                   g_last_error;
 static WsClient g_ws;
 
 // Toggles de paneles (visibles desde el menu View del menubar canonico)
-static bool g_show_main = true;
-static bool g_show_live = true;
+static bool g_show_main       = false;  // diagnostico, off por defecto
+static bool g_show_live       = true;
+static bool g_show_dag_list   = true;
+static bool g_show_dag_detail = true;
+static bool g_show_run_detail = true;
+
+// Auto-fetch DAG list una vez al arrancar.
+static bool g_initial_fetched = false;
 
 // Upsert por id en g_live_runs.
 static void upsert_live_run(const dag_ui::DagRunRow& r) {
@@ -115,6 +122,12 @@ static void draw_live() {
 }
 
 static void render() {
+    // Auto-fetch DAGs on first frame.
+    if (!g_initial_fetched) {
+        g_initial_fetched = true;
+        dag_ui::list_dags_http(g_api_url, g_dags);
+    }
+
     // Drain WS messages this frame (cheap, max 64).
     {
         std::vector<std::string> msgs;
@@ -122,8 +135,11 @@ static void render() {
         for (auto& m : msgs) parse_ws_payload(m);
     }
 
-    if (g_show_main) draw_main();
-    if (g_show_live) draw_live();
+    if (g_show_dag_list)   dag_ui_tabs::draw_dag_list(g_api_url, g_dags, g_live_runs);
+    if (g_show_dag_detail) dag_ui_tabs::draw_dag_detail(g_api_url);
+    if (g_show_run_detail) dag_ui_tabs::draw_run_detail(g_api_url);
+    if (g_show_main)       draw_main();
+    if (g_show_live)       draw_live();
 }
 
 int main(int /*argc*/, char** /*argv*/) {
@@ -131,8 +147,11 @@ int main(int /*argc*/, char** /*argv*/) {
     g_ws.start(g_ws_host, g_ws_port, g_ws_path);
 
     static fn_ui::PanelToggle panels[] = {
-        { "Main", nullptr, &g_show_main },
-        { "Live (WS)", nullptr, &g_show_live },
+        { "DAGs",        nullptr, &g_show_dag_list },
+        { "DAG Detail",  nullptr, &g_show_dag_detail },
+        { "Run Detail",  nullptr, &g_show_run_detail },
+        { "Live (WS)",   nullptr, &g_show_live },
+        { "Main (diag)", nullptr, &g_show_main },
     };
 
     fn::AppConfig cfg;