[management,client] Default to NetBird's upload service when nothing is configured

The previous commit made a peer with no destination — no MDM override, no URL
named by the caller, nothing published by its management server — refuse to
upload and keep the bundle local unless it was enrolled with NetBird's cloud.
That closed the reported data-boundary concern, but it broke the default for
everyone who uploads a bundle as part of their day: a self-hosted user opening
a support ticket got a refusal where the command used to work.

Product decision (NetBird's, not the reporter's): the knob to keep bundles
inside your own infrastructure is what this branch provides, and it is enough.
The default stays the service NetBird runs, self-hosted included. An admin who
needs the bundles to stay in-house configures the destination; until then the
everyday flow keeps working.

So ResolveUploadURL drops the cloud check, the sentinel error and the
managementURL argument, and never fails:

    MDM  >  explicitly named URL  >  published by management  >  NetBird's service

Nothing observable changes for a deployment that configures nothing, which also
removes two edge cases the fail-closed default had: a peer still enrolled on the
legacy api.wiretrustee.com host would have been classified self-hosted and
refused, and an upgrade would have silently stopped uploads for self-hosted
deployments relying on them. The privilege gate is unaffected — a host other
than the default one still requires a privileged caller, so pointing the CLI
somewhere other than what management published needs root.

client/internal/engine.go

@@ -230,9 +230,8 @@ type Engine struct {
 	// debugUploadURL is the debug-bundle upload service the management server
 	// publishes for this deployment, refreshed on every NetbirdConfig update.
 	// Atomic because the bundle paths (remote job, daemon RPC, mobile SDK) read
-	// it off the engine loop. Empty when the deployment publishes none, which is
-	// what makes a self-hosted peer keep its bundle local instead of shipping it
-	// to the upload service NetBird runs.
+	// it off the engine loop. Empty when the deployment publishes none, in which
+	// case the callers fall back to the service NetBird runs.
 	debugUploadURL atomic.Pointer[string]
 
 	clientCtx    context.Context
@@ -1243,8 +1242,8 @@ func (e *Engine) handleDebugUploadUpdate(config *mgmProto.DebugConfig) {
 
 // DebugUploadURL returns the debug-bundle upload service the management server
 // published, or empty when it published none or the engine never synced. The
-// callers treat empty as "no destination from this deployment" and fail closed
-// unless the peer is enrolled with NetBird's cloud; see debug.ResolveUploadURL.
+// callers treat empty as "this deployment names no destination" and fall back to
+// the service NetBird runs; see debug.ResolveUploadURL.
 func (e *Engine) DebugUploadURL() string {
 	if url := e.debugUploadURL.Load(); url != nil {
 		return *url
@@ -1466,10 +1465,8 @@ func (e *Engine) handleBundle(params *mgmProto.BundleParameters) (*mgmProto.JobR
 
 	// Resolve the upload destination: an MDM override, when set, takes
 	// precedence over the job's URL. Both are validated the same way. With
-	// neither, the destination this deployment publishes is used, and only a
-	// peer enrolled with NetBird's cloud falls back to the service NetBird runs
-	// — a self-hosted deployment that named no upload service gets no upload
-	// rather than one that leaves the operator's control sphere.
+	// neither, the destination this deployment publishes is used, and failing
+	// that the service NetBird runs.
 	uploadURL := params.GetUploadUrl()
 	if override := e.config.ProfileConfig.DebugBundleUploadURL; override != "" {
 		log.Infof("using MDM debug bundle upload URL override instead of the management-supplied value")
@@ -1479,10 +1476,7 @@ func (e *Engine) handleBundle(params *mgmProto.BundleParameters) (*mgmProto.JobR
 		return nil, err
 	}
 
-	uploadURL, err = debug.ResolveUploadURL(uploadURL, e.DebugUploadURL(), e.config.ProfileConfig.ManagementURL.String())
-	if err != nil {
-		return nil, err
-	}
+	uploadURL = debug.ResolveUploadURL(uploadURL, e.DebugUploadURL())
 
 	bundleDeps := debug.GeneratorDependencies{
 		InternalConfig: e.config.ProfileConfig,