feat(tailscale): add Tailscale control center widget (#1875)

* feat(tailscale): add Tailscale control center widget

Full-stack Tailscale integration for DMS control center:

Backend (Go):
- Event-driven manager via WatchIPNBus (no polling)
- Reconnects with exponential backoff when tailscaled unavailable
- Typed conversion from ipnstate.Status to QML-friendly IPC types
- Testable via tailscaleClient interface with mock watcher
- Manager cleanup in cleanupManagers()
- 19 unit tests

Frontend (QML):
- TailscaleService with WebSocket subscription
- TailscaleWidget with peer list, filter chips, search
- Copy-to-clipboard for IPs and DNS names
- Daemon lifecycle handling (offline/stopped states)

Dependencies:
- Add tailscale.com v1.96.1 (official local API client)
- Bump Go to 1.26.1 (required by tailscale.com)

* cleanups

---------

Co-authored-by: bbedward <bbedward@gmail.com>

quickshell/Modules/ControlCenter/Components/DragDropGrid.qml

@@ -918,6 +918,12 @@ Column {
                     }
                     builtinInstance = Qt.binding(() => root.model?.cupsBuiltinInstance);
                 }
+                if (id === "builtin_tailscale") {
+                    if (root.model?.tailscaleLoader) {
+                        root.model.tailscaleLoader.active = true;
+                    }
+                    builtinInstance = Qt.binding(() => root.model?.tailscaleBuiltinInstance);
+                }
             }
 
             sourceComponent: {