Wire Chromium browser into UI with command palette entry

- BrowserPanelView: branches on panel.engineType to show either
  the existing WebViewRepresentable (WebKit) or the new
  CEFBrowserViewRepresentable (Chromium). Falls back to
  CEFDownloadView if CEF isn't initialized.

- CEFBrowserViewRepresentable: NSViewRepresentable that hosts
  a CEFBrowserView in SwiftUI.

- AppDelegate: added openChromiumBrowserAndFocusAddressBar() that
  finds or creates a Chromium profile and opens a browser tab.

- ContentView: added "New Tab (Chromium Browser)" command palette
  entry (palette.newChromiumBrowserTab).

Users can now open a Chromium-engine browser tab via the command
palette. The tab shows the CEF download UI if the framework isn't
available, or renders pages via Chromium if it is.

Author: lawrencecchen

GhosttyTabs.xcodeproj/project.pbxproj

@@ -12,6 +12,7 @@
 		CEF00003 /* CEFRuntime.swift in Sources */ = {isa = PBXBuildFile; fileRef = CEF00013 /* CEFRuntime.swift */; };
 		CEF00004 /* CEFDownloadView.swift in Sources */ = {isa = PBXBuildFile; fileRef = CEF00014 /* CEFDownloadView.swift */; };
 		CEF00005 /* CEFBrowserView.swift in Sources */ = {isa = PBXBuildFile; fileRef = CEF00015 /* CEFBrowserView.swift */; };
+		CEF00006 /* CEFBrowserViewRepresentable.swift in Sources */ = {isa = PBXBuildFile; fileRef = CEF00016 /* CEFBrowserViewRepresentable.swift */; };
 			A5001001 /* cmuxApp.swift in Sources */ = {isa = PBXBuildFile; fileRef = A5001011 /* cmuxApp.swift */; };
 			A5001002 /* ContentView.swift in Sources */ = {isa = PBXBuildFile; fileRef = A5001012 /* ContentView.swift */; };
 			E62155868BB29FEB5DAAAF25 /* SidebarSelectionState.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9AD52285508B1D6A9875E7B3 /* SidebarSelectionState.swift */; };
@@ -186,6 +187,7 @@
 		CEF00013 /* CEFRuntime.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BrowserEngine/CEFRuntime.swift; sourceTree = "<group>"; };
 		CEF00014 /* CEFDownloadView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BrowserEngine/CEFDownloadView.swift; sourceTree = "<group>"; };
 		CEF00015 /* CEFBrowserView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BrowserEngine/CEFBrowserView.swift; sourceTree = "<group>"; };
+		CEF00016 /* CEFBrowserViewRepresentable.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BrowserEngine/CEFBrowserViewRepresentable.swift; sourceTree = "<group>"; };
 			A5001000 /* cmux.app */ = {isa = PBXFileReference; explicitFileType = wrapper.application; includeInIndex = 0; path = cmux.app; sourceTree = BUILT_PRODUCTS_DIR; };
 			F1000002A1B2C3D4E5F60718 /* cmuxTests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = cmuxTests.xctest; sourceTree = BUILT_PRODUCTS_DIR; };
 			7E7E6EF344A568AC7FEE3715 /* cmuxUITests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = cmuxUITests.xctest; sourceTree = BUILT_PRODUCTS_DIR; };
@@ -473,6 +475,7 @@
 				CEF00013 /* CEFRuntime.swift */,
 				CEF00014 /* CEFDownloadView.swift */,
 				CEF00015 /* CEFBrowserView.swift */,
+				CEF00016 /* CEFBrowserViewRepresentable.swift */,
 			);
 			path = Sources;
 			sourceTree = "<group>";
@@ -773,6 +776,7 @@
 				CEF00003 /* CEFRuntime.swift in Sources */,
 				CEF00004 /* CEFDownloadView.swift in Sources */,
 				CEF00005 /* CEFBrowserView.swift in Sources */,
+				CEF00006 /* CEFBrowserViewRepresentable.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

Sources/AppDelegate.swift

@@ -9904,6 +9904,32 @@ final class AppDelegate: NSObject, NSApplicationDelegate, UNUserNotificationCent
         return panelId
     }
 
+    /// Open a browser tab using the Chromium engine. Creates a Chromium
+    /// profile if none exists, then opens a browser tab with that profile.
+    @discardableResult
+    func openChromiumBrowserAndFocusAddressBar(url: URL? = nil) -> UUID? {
+        let store = BrowserProfileStore.shared
+        // Find or create a Chromium profile
+        let chromiumProfile: BrowserProfileDefinition
+        if let existing = store.profiles.first(where: { $0.engineType == .chromium }) {
+            chromiumProfile = existing
+        } else {
+            guard let created = store.createProfile(named: "Chromium", engineType: .chromium) else {
+                return nil
+            }
+            chromiumProfile = created
+        }
+
+        guard let panelId = tabManager?.openBrowser(
+            url: url,
+            preferredProfileID: chromiumProfile.id,
+            insertAtEnd: true
+        ) else { return nil }
+
+        _ = focusBrowserAddressBar(panelId: panelId)
+        return panelId
+    }
+
     private func focusBrowserAddressBar(in panel: BrowserPanel) {
 #if DEBUG
         let requestId = panel.requestAddressBarFocus()

Sources/BrowserEngine/CEFBrowserViewRepresentable.swift

@@ -0,0 +1,15 @@
+import SwiftUI
+import AppKit
+
+/// NSViewRepresentable that hosts a CEFBrowserView in SwiftUI.
+struct CEFBrowserViewRepresentable: NSViewRepresentable {
+    let cefBrowserView: CEFBrowserView
+
+    func makeNSView(context: Context) -> CEFBrowserView {
+        cefBrowserView
+    }
+
+    func updateNSView(_ nsView: CEFBrowserView, context: Context) {
+        // Layout is handled by autoresizing masks and CEFBrowserView.layout()
+    }
+}

Sources/ContentView.swift

@@ -5342,6 +5342,14 @@ struct ContentView: View {
                 keywords: ["new", "browser", "tab", "web"]
             )
         )
+        contributions.append(
+            CommandPaletteCommandContribution(
+                commandId: "palette.newChromiumBrowserTab",
+                title: constant(String(localized: "command.newChromiumBrowserTab.title", defaultValue: "New Tab (Chromium Browser)")),
+                subtitle: constant(String(localized: "command.newChromiumBrowserTab.subtitle", defaultValue: "Tab")),
+                keywords: ["new", "chromium", "browser", "tab", "web", "chrome", "extension"]
+            )
+        )
         contributions.append(
             CommandPaletteCommandContribution(
                 commandId: "palette.closeTab",
@@ -6000,6 +6008,11 @@ struct ContentView: View {
                 _ = AppDelegate.shared?.openBrowserAndFocusAddressBar()
             }
         }
+        registry.register(commandId: "palette.newChromiumBrowserTab") {
+            DispatchQueue.main.async {
+                _ = AppDelegate.shared?.openChromiumBrowserAndFocusAddressBar()
+            }
+        }
         registry.register(commandId: "palette.closeTab") {
             tabManager.closeCurrentPanelWithConfirmation()
         }

Sources/Panels/BrowserPanelView.swift

@@ -1117,7 +1117,9 @@ struct BrowserPanelView: View {
             isCurrentPaneOwner
 
         return Group {
-            if panel.shouldRenderWebView {
+            if panel.engineType == .chromium {
+                chromiumWebView
+            } else if panel.shouldRenderWebView {
                 WebViewRepresentable(
                     panel: panel,
                     paneId: paneId,
@@ -1189,6 +1191,34 @@ struct BrowserPanelView: View {
         .zIndex(0)
     }
 
+    /// View for Chromium-engine browser panels. Shows the CEFBrowserView
+    /// if CEF is initialized, or the download/error UI otherwise.
+    @ViewBuilder
+    private var chromiumWebView: some View {
+        if let cefView = panel.cefBrowserView, CEFRuntime.shared.isInitialized {
+            CEFBrowserViewRepresentable(cefBrowserView: cefView)
+                .accessibilityIdentifier("ChromiumBrowserView")
+        } else if !CEFRuntime.shared.isInitialized {
+            CEFDownloadView {
+                // User cancelled, nothing to do
+            }
+        } else {
+            VStack {
+                Text(String(
+                    localized: "cef.error.title",
+                    defaultValue: "Chromium engine unavailable"
+                ))
+                .font(.headline)
+                if let error = CEFRuntime.shared.initError {
+                    Text(error)
+                        .font(.caption)
+                        .foregroundStyle(.secondary)
+                }
+            }
+            .frame(maxWidth: .infinity, maxHeight: .infinity)
+        }
+    }
+
     private func triggerFocusFlashAnimation() {
         focusFlashAnimationGeneration &+= 1
         let generation = focusFlashAnimationGeneration