feat(tsconnect): add getCert, listenTLS, setFunnel + fix TLS cert for WASM

Enable ACME TLS certificates on js/wasm by dropping the !js build tag from
cert.go and routing storage through the state store. Add getCert, listenTLS,
and setFunnel WASM bindings with a combinedTLSListener that merges Funnel
ingress and direct tailnet connections. Notify the control plane immediately
after serve config changes to accelerate Funnel DNS provisioning.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ipn/ipnlocal/cert.go

@@ -1,7 +1,7 @@
 // Copyright (c) Tailscale Inc & contributors
 // SPDX-License-Identifier: BSD-3-Clause
 
-//go:build !js && !ts_omit_acme
+//go:build !ts_omit_acme
 
 package ipnlocal
 
@@ -302,6 +302,9 @@ var errCertExpired = errors.New("cert expired")
 var testX509Roots *x509.CertPool // set non-nil by tests
 
 func (b *LocalBackend) getCertStore() (certStore, error) {
+	if runtime.GOOS == "js" {
+		return certStateStore{StateStore: b.store}, nil
+	}
 	switch b.store.(type) {
 	case *store.FileStore:
 	case *mem.Store:
@@ -333,6 +336,16 @@ func (b *LocalBackend) ConfigureCertsForTest(getCert func(hostname string) (*TLS
 	b.mu.Unlock()
 }
 
+// SetACMEHTTPClient sets a custom HTTP client for ACME certificate operations.
+// On js/wasm, this can be used to route requests through the Tailscale network
+// stack to bypass browser CORS if Let's Encrypt endpoints fail preflight.
+// A nil value (the default) uses the standard http.DefaultClient.
+func (b *LocalBackend) SetACMEHTTPClient(c *http.Client) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.acmeHTTPClient = c
+}
+
 // certFileStore implements certStore by storing the cert & key files in the named directory.
 type certFileStore struct {
 	dir string
@@ -550,6 +563,9 @@ var getCertPEM = func(ctx context.Context, b *LocalBackend, cs certStore, logf l
 	if err != nil {
 		return nil, err
 	}
+	b.mu.Lock()
+	ac.HTTPClient = b.acmeHTTPClient
+	b.mu.Unlock()
 
 	if !isDefaultDirectoryURL(ac.DirectoryURL) {
 		logf("acme: using Directory URL %q", ac.DirectoryURL)