refactor(shaders_lab): migrar layouts inline a layout_storage publico

Sustituye ~30 lineas de cableado manual de save/load/list/delete contra
layout_storage_sqlite por dos llamadas a la nueva API publica:

    g_layouts = fn_ui::layout_storage_open("shaders_lab.db");
    fn_ui::layout_storage_make_callbacks(g_layouts, g_layout_cb);

El blob pendiente lo gestiona el storage (layout_storage_apply_pending).
on_reset se override para ademas re-mostrar los paneles de shaders_lab.
La tabla ui_layouts heredada queda intacta — la nueva API usa
imgui_layouts en la misma BD.

cpp/apps/shaders_lab/CMakeLists.txt

@@ -16,8 +16,8 @@ add_imgui_app(shaders_lab
     ${CMAKE_SOURCE_DIR}/functions/gfx/dag_node_previews.cpp
     ${CMAKE_SOURCE_DIR}/functions/gfx/shaderlab_db.cpp
     ${CMAKE_SOURCE_DIR}/functions/gfx/code_to_generator.cpp
-    # fps_overlay, panel_menu, layouts_menu, app_menubar ya viven en fn_framework
-    ${CMAKE_SOURCE_DIR}/functions/core/layout_storage_sqlite.cpp
+    # fps_overlay, panel_menu, layouts_menu, app_menubar, layout_storage ya
+    # viven en fn_framework.
 )
 target_include_directories(shaders_lab PRIVATE
     ${CMAKE_CURRENT_SOURCE_DIR}

cpp/apps/shaders_lab/main.cpp

@@ -17,7 +17,7 @@
 #include "core/panel_menu.h"
 #include "core/layouts_menu.h"
 #include "core/app_menubar.h"
-#include "core/layout_storage_sqlite.h"
+#include "core/layout_storage.h"
 
 #include <chrono>
 #include <cctype>
@@ -71,9 +71,10 @@ static bool g_show_functions = true;
 static bool g_show_generated = true;
 
 // ── Layouts (named ImGui ini snapshots persisted in shaders_lab.db) ───────
+// El storage opaco encapsula la BD y el blob pendiente. Los callbacks
+// envuelven save/apply/delete/reset y se pasan a app_menubar tal cual.
+static fn_ui::LayoutStorage*  g_layouts = nullptr;
 static fn_ui::LayoutCallbacks g_layout_cb;
-static std::string g_pending_layout_blob; // applied at start of next frame
-static std::string g_pending_layout_name; // becomes active_name after apply
 
 // ── Save-as-generator modal state ─────────────────────────────────────────
 static bool   g_save_modal_open = false;
@@ -222,13 +223,8 @@ static void load_user_generators_into_catalog() {
 static void render() {
     // Apply pending layout BEFORE any ImGui::Begin this frame.
     // (LoadIniSettingsFromMemory must happen before windows are submitted.)
-    if (!g_pending_layout_blob.empty()) {
-        ImGui::LoadIniSettingsFromMemory(g_pending_layout_blob.c_str(),
-                                         g_pending_layout_blob.size());
-        g_layout_cb.active_name = g_pending_layout_name;
-        g_pending_layout_blob.clear();
-        g_pending_layout_name.clear();
-    }
+    std::string applied = fn_ui::layout_storage_apply_pending(g_layouts);
+    if (!applied.empty()) g_layout_cb.active_name = applied;
 
     if (!g_canvas_code.initialized) fn::gfx::canvas_init(g_canvas_code);
     if (!g_canvas_dag.initialized)  fn::gfx::canvas_init(g_canvas_dag);
@@ -412,37 +408,20 @@ int main() {
     load_user_generators_into_catalog();
     ensure_dag_default();
 
-    // Layout persistence on the same shaders_lab.db connection.
-    sqlite3* db = fn::gfx::shaderlab_db_handle();
-    fn_ui::layout_storage_init(db);
+    // Layout persistence: handle opaco que crea su propia tabla
+    // imgui_layouts en shaders_lab.db (CREATE IF NOT EXISTS, no toca la
+    // tabla ui_layouts heredada). Cualquier app del registry puede usar
+    // este patron.
+    g_layouts = fn_ui::layout_storage_open("shaders_lab.db");
+    fn_ui::layout_storage_make_callbacks(g_layouts, g_layout_cb);
 
-    g_layout_cb.list = [db]() {
-        return fn_ui::layout_storage_list(db);
-    };
-    g_layout_cb.on_apply = [db](const std::string& name) {
-        std::string blob = fn_ui::layout_storage_load_blob(db, name);
-        if (!blob.empty()) {
-            g_pending_layout_blob = std::move(blob);
-            g_pending_layout_name = name;
-        }
-    };
-    g_layout_cb.on_save = [db](const std::string& name) {
-        size_t size = 0;
-        const char* blob = ImGui::SaveIniSettingsToMemory(&size);
-        if (blob && size > 0) {
-            fn_ui::layout_storage_save(db, name, std::string(blob, size));
-            g_layout_cb.active_name = name;
-        }
-    };
-    g_layout_cb.on_delete = [db](const std::string& name) {
-        fn_ui::layout_storage_delete(db, name);
-        if (g_layout_cb.active_name == name) g_layout_cb.active_name.clear();
-    };
+    // Override de on_reset: ademas de limpiar el INI, re-mostrar todos
+    // los paneles especificos de shaders_lab.
     g_layout_cb.on_reset = []() {
-        // Default reset: open every panel and clear active layout marker.
-        // The actual dock layout is whatever ImGui rebuilt on first launch.
         g_show_code = g_show_dag = g_show_canvas_c = g_show_canvas_d =
             g_show_controls = g_show_functions = g_show_generated = true;
+        ImGui::LoadIniSettingsFromMemory("", 0);
+        ImGui::GetIO().WantSaveIniSettings = true;
         g_layout_cb.active_name.clear();
     };
 
@@ -456,6 +435,7 @@ int main() {
     fn::gfx::canvas_destroy(g_canvas_dag);
     fn::gfx::dag_node_editor_destroy();
     fn::gfx::dag_previews_destroy();
+    fn_ui::layout_storage_close(g_layouts);
     fn::gfx::shaderlab_db_close();
     return rc;
 }