Add NebulaController, tab manager, and CEF clients

Introduce core application structure and browser management: add NebulaController and run entry (src/app/*) to centralize window, tab and CEF lifecycle logic; implement TabManager and NebulaTab (src/browser/*) for tab creation, navigation and state tracking; add URL utilities (NormalizeNavigationInput, JsonEscape) and CEF browser client glue (src/cef/browser_client.cpp/.h) to forward chrome commands and content events. Update app/main.cpp to delegate startup to nebula::app::RunNebula. Add UI assets (chrome.html, chrome.css, chrome.js, lucide, menu-popup updates) and remove obsolete nebot.html. Update CMakeLists to include new sources, add ${CMAKE_SOURCE_DIR}/src to includes and link dwmapi on Windows. Overall this refactors startup and splits responsibilities for cleaner tab and browser lifecycle handling.

src/app/run.cpp

@@ -0,0 +1,54 @@
+#include "app/run.h"
+
+#include "app/nebula_controller.h"
+#include "cef/nebula_app.h"
+#include "include/cef_app.h"
+#include "include/cef_command_line.h"
+#include "ui/paths.h"
+
+namespace nebula::app {
+namespace {
+
+void EnableDpiAwareness() {
+    SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);
+}
+
+}  // namespace
+
+int RunNebula(HINSTANCE instance, int show_command) {
+    EnableDpiAwareness();
+
+    CefMainArgs main_args(instance);
+    CefRefPtr<nebula::cef::NebulaApp> app(new nebula::cef::NebulaApp);
+
+    const int subprocess_exit_code = CefExecuteProcess(main_args, app, nullptr);
+    if (subprocess_exit_code >= 0) {
+        return subprocess_exit_code;
+    }
+
+    CefSettings settings;
+    settings.no_sandbox = true;
+
+    if (!CefInitialize(main_args, settings, app, nullptr)) {
+        return CefGetExitCode();
+    }
+
+    CefRefPtr<CefCommandLine> command_line = CefCommandLine::CreateCommandLine();
+    command_line->InitFromString(GetCommandLineW());
+
+    std::string initial_url = command_line->GetSwitchValue("url");
+    if (nebula::ui::IsEmptyOrChromiumNewTabUrl(initial_url)) {
+        initial_url = nebula::ui::GetHomeUrl();
+    }
+
+    NebulaController controller(instance, initial_url, show_command);
+    const bool created = controller.Create();
+    if (created) {
+        CefRunMessageLoop();
+    }
+
+    CefShutdown();
+    return created ? 0 : 1;
+}
+
+}  // namespace nebula::app