Open cmd+clicked terminal links in cmux browser panel (#53)

* Open cmd+clicked terminal links in cmux browser panel instead of system browser

Handle GHOSTTY_ACTION_OPEN_URL in the Ghostty action callback to intercept
link opens. Uses preferredBrowserTargetPane to reuse an existing right-side
pane, falling back to a new horizontal split.

* Use tab-specific manager for OPEN_URL action

Use tabManagerFor(tabId:) instead of the active-window tabManager so the
lookup succeeds when the surface belongs to a different window context.

Sources/GhosttyTerminalView.swift

@@ -888,6 +888,25 @@ class GhosttyApp {
                 surfaceView.updateKeyTable(action.action.key_table)
                 return true
             }
+        case GHOSTTY_ACTION_OPEN_URL:
+            let openUrl = action.action.open_url
+            guard let cstr = openUrl.url else { return false }
+            let urlString = String(cString: cstr)
+            guard let url = URL(string: urlString) else { return false }
+            guard let tabId = surfaceView.tabId,
+                  let surfaceId = surfaceView.terminalSurface?.id else { return false }
+            return performOnMain {
+                guard let app = AppDelegate.shared,
+                      let tabManager = app.tabManagerFor(tabId: tabId) ?? app.tabManager,
+                      let workspace = tabManager.tabs.first(where: { $0.id == tabId }) else {
+                    return false
+                }
+                if let targetPane = workspace.preferredBrowserTargetPane(fromPanelId: surfaceId) {
+                    return workspace.newBrowserSurface(inPane: targetPane, url: url, focus: true) != nil
+                } else {
+                    return workspace.newBrowserSplit(from: surfaceId, orientation: .horizontal, url: url) != nil
+                }
+            }
         default:
             return false
         }

TODO.md

@@ -47,6 +47,10 @@
 - [ ] Add question mark icon to learn shortcuts
 - [ ] Notification popover: each button item should show outline outside when focused/hovered
 - [ ] Notification popover: add right-click context menu to mark as read/unread
+- [ ] Cmd+click should open links in cmux (browser panel) instead of external browser
+- [ ] "Waiting for input" notification should include custom terminal title if set
+- [ ] Close button for current/active tab should always be visible (not just on hover)
+- [ ] Add browser icon to the left of the plus button in the tab bar
 
 ## Analytics
 - [x] Add PostHog tracking (set `PostHogAnalytics.apiKey` in `Sources/PostHogAnalytics.swift`)