[management] Move the activity policy out of the gRPC service

Recording proxy usage is business logic, and it had ended up in the RPC
handler: the throttle interval, the service-user skip, the exclusion rule
for embedded and browser peers, and a store handle to write through.

It moves to a reverseproxy module manager, matching how accesslogs, domain,
service and proxy are already structured, and the RPC keeps only what is
its own: calling the manager and deciding the request must not fail when
the write does. The proxy service goes back to holding ProxyTokenChecker
rather than a widened store interface.

The policy tests move with the policy. The handler tests now assert only
that a granted request reaches the manager, which is all the transport
decides.

management/internals/modules/reverseproxy/activity/interface.go

@@ -0,0 +1,25 @@
+// Package activity records that a principal used a reverse proxy service, so
+// that activity accounting counts people and devices which reach services
+// through the proxy but never touch the dashboard or the management API.
+package activity
+
+import (
+	"context"
+
+	"github.com/netbirdio/netbird/management/server/peer"
+	"github.com/netbirdio/netbird/management/server/types"
+)
+
+// Manager records reverse proxy usage against the timestamps activity
+// accounting reads. Both methods are best effort from the caller's point of
+// view: a lost record is corrected by the next request, and no authorization
+// decision reads them back.
+type Manager interface {
+	// RecordUserLogin records a completed SSO sign-in to a proxied service.
+	// Service users have no interactive login and are ignored.
+	RecordUserLogin(ctx context.Context, accountID string, user *types.User) error
+	// RecordPeerSeen records that a peer reached a private service over the
+	// mesh, which is what lets its owner count as active. Peers activity
+	// accounting excludes, and peers already seen recently, are ignored.
+	RecordPeerSeen(ctx context.Context, accountID string, peer *peer.Peer) error
+}