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>

core/internal/server/tailscale/handlers.go

@@ -0,0 +1,30 @@
+package tailscale
+
+import (
+	"fmt"
+	"net"
+
+	"github.com/AvengeMedia/DankMaterialShell/core/internal/server/models"
+)
+
+// HandleRequest routes an IPC request to the appropriate handler.
+func HandleRequest(conn net.Conn, req models.Request, manager *Manager) {
+	switch req.Method {
+	case "tailscale.getStatus":
+		handleGetStatus(conn, req, manager)
+	case "tailscale.refresh":
+		handleRefresh(conn, req, manager)
+	default:
+		models.RespondError(conn, req.ID, fmt.Sprintf("unknown method: %s", req.Method))
+	}
+}
+
+func handleGetStatus(conn net.Conn, req models.Request, manager *Manager) {
+	state := manager.GetState()
+	models.Respond(conn, req.ID, state)
+}
+
+func handleRefresh(conn net.Conn, req models.Request, manager *Manager) {
+	manager.RefreshState()
+	models.Respond(conn, req.ID, models.SuccessResult{Success: true, Message: "refreshed"})
+}