Enable GPU/WebGL and add persistent cache dirs

Enable hardware-accelerated rendering and persist GPU/cache data. Added a BrowserSettings() helper that enables WebGL and use it when creating Chrome/Content/MenuPopup browsers (src/app/nebula_controller.cpp). Configure CefSettings to use a persistent user data and cache directory (src/app/run.cpp) by calling nebula::ui::GetUserDataDirectory() and GetCacheDirectory(). Add command-line switches to initialize the GPU process and avoid sandbox/blocklist fallbacks (disable GPU sandbox, in-process-gpu, ignore-gpu-blocklist, enable-accelerated-video-decode, use ANGLE D3D11) to prevent GPU crashes and Chromium falling back to software rendering (src/cef/nebula_app.cpp). Implement GetUserDataDirectory() and GetCacheDirectory() (preferring %LOCALAPPDATA% with an executable-directory fallback) and expose them in the header (src/ui/paths.cpp, src/ui/paths.h). These changes ensure GPU shader caching, WebGL support, and smoother video/graphics behavior.

src/app/run.cpp

@@ -29,6 +29,19 @@ int RunNebula(HINSTANCE instance, int show_command) {
     CefSettings settings;
     settings.no_sandbox = true;
 
+    // A persistent profile is required for the GPU shader cache and several
+    // hardware acceleration features. Without these Chromium silently falls
+    // back to software rendering, which causes choppy video and disables
+    // WebGL/WebGL2 in the GPU diagnostics page.
+    const std::wstring user_data_dir = nebula::ui::GetUserDataDirectory().wstring();
+    const std::wstring cache_dir = nebula::ui::GetCacheDirectory().wstring();
+    if (!user_data_dir.empty()) {
+        CefString(&settings.root_cache_path).FromWString(user_data_dir);
+    }
+    if (!cache_dir.empty()) {
+        CefString(&settings.cache_path).FromWString(cache_dir);
+    }
+
     if (!CefInitialize(main_args, settings, app, nullptr)) {
         return CefGetExitCode();
     }