Add host platform detection and macOS styles

Expose host platform to the UI and apply platform-specific styling. Backend: add CurrentPlatformName() and include "platform" in the JSON sent from NebulaController so the frontend can know the host OS. Frontend: detectHostPlatform() initializes state.platform, applyPlatform() sets a platform-* body class, and applyState() applies it. CSS: add .platform-macos rules to adjust title padding and hide window controls on macOS. Also fix FilePathToUrl to avoid producing an extra slash when the encoded path already starts with '/'.

src/app/nebula_controller.cpp

@@ -165,6 +165,18 @@ std::string GetChromeDisplayUrl(const std::string& url) {
     return nebula::ui::IsInternalHomeUrl(url) ? std::string{} : url;
 }
 
+const char* CurrentPlatformName() {
+#if defined(_WIN32)
+    return "windows";
+#elif defined(__APPLE__)
+    return "macos";
+#elif defined(__linux__)
+    return "linux";
+#else
+    return "unknown";
+#endif
+}
+
 void SetBrowserVisible(CefRefPtr<CefBrowser> browser, bool visible) {
     if (!browser) {
         return;
@@ -1127,6 +1139,7 @@ void NebulaController::SendChromeState(const nebula::browser::NebulaTab& tab) {
         ",\"canGoForward\":" + std::string(tab.CanGoForward() ? "true" : "false") +
         ",\"favicon\":\"" + nebula::browser::JsonEscape(tab.favicon_url) + "\"" +
         ",\"zoomLevel\":" + std::to_string(zoom_level) +
+        ",\"platform\":\"" + CurrentPlatformName() + "\"" +
         ",\"tabs\":" + tabs_json +
         "});";
 

src/ui/paths.cpp

@@ -174,7 +174,7 @@ std::string FilePathToUrl(std::filesystem::path path) {
     for (char ch : value) {
         encoded += ch == ' ' ? "%20" : std::string(1, ch);
     }
-    return "file:///" + encoded;
+    return encoded.starts_with('/') ? "file://" + encoded : "file:///" + encoded;
 }
 
 std::string GetChromeUrl() {

ui/css/chrome.css

@@ -89,6 +89,10 @@ button:disabled {
   background: var(--bg);
 }
 
+.platform-macos .title-row {
+  padding: 0 12px 0 78px;
+}
+
 /* ── Tabs ───────────────────────────────────────────────────── */
 
 .tabs {
@@ -257,6 +261,10 @@ button:disabled {
   color: white;
 }
 
+.platform-macos .window-controls {
+  display: none;
+}
+
 /* ── Toolbar ────────────────────────────────────────────────── */
 
 .toolbar {

ui/js/chrome.js

@@ -28,9 +28,24 @@ const state = {
   canGoBack: false,
   canGoForward: false,
   favicon: '',
+  platform: detectHostPlatform(),
   tabs: []
 };
 
+function detectHostPlatform() {
+  const platform = `${navigator.userAgentData?.platform || ''} ${navigator.platform || ''} ${navigator.userAgent || ''}`.toLowerCase();
+  if (platform.includes('mac')) return 'macos';
+  if (platform.includes('win')) return 'windows';
+  if (platform.includes('linux')) return 'linux';
+  return 'unknown';
+}
+
+function applyPlatform(platform) {
+  const normalized = ['macos', 'windows', 'linux'].includes(platform) ? platform : 'unknown';
+  document.body.classList.remove('platform-macos', 'platform-windows', 'platform-linux', 'platform-unknown');
+  document.body.classList.add(`platform-${normalized}`);
+}
+
 function hexToRgb(hex) {
   if (!hex || typeof hex !== 'string') return null;
   let normalized = hex.trim().replace(/^#/, '');
@@ -191,6 +206,7 @@ function renderTabs() {
 
 function applyState(nextState) {
   Object.assign(state, nextState || {});
+  applyPlatform(state.platform);
 
   const title = state.title || 'New Tab';
   const url = state.url || '';