* [management] Add metrics for peer status updates and ephemeral cleanup
The session-fenced MarkPeerConnected / MarkPeerDisconnected path and
the ephemeral peer cleanup loop both run silently today: when fencing
rejects a stale stream, when a cleanup tick deletes peers, or when a
batch delete fails, we have no operational signal beyond log lines.
Add OpenTelemetry counters and a histogram so the same SLO-style
dashboards that already exist for the network-map controller can cover
peer connect/disconnect and ephemeral cleanup too.
All new attributes are bounded enums: operation in {connect,disconnect}
and outcome in {applied,stale,error,peer_not_found}. No account, peer,
or user ID is ever written as a metric label — total cardinality is
fixed at compile time (8 counter series, 2 histogram series, 4 unlabeled
ephemeral series).
Metric methods are nil-receiver safe so test composition that doesn't
wire telemetry (the bulk of the existing tests) works unchanged. The
ephemeral manager exposes a SetMetrics setter rather than taking the
collector through its constructor, keeping the constructor signature
stable across all test call sites.
* [management] Add OpenTelemetry metrics for ephemeral peer cleanup
Introduce counters for tracking ephemeral peer cleanup, including peers pending deletion, cleanup runs, successful deletions, and failed batches. Metrics are nil-receiver safe to ensure compatibility with test setups without telemetry.
* Unified NetBird combined server (Management, Signal, Relay, STUN) as a single executable with richer YAML configuration, validation, and defaults.
* Official Dockerfile/image for single-container deployment.
* Optional in-process profiling endpoint for diagnostics.
* Multiplexing to route HTTP/gRPC/WebSocket traffic via one port; runtime hooks to inject custom handlers.
* **Chores**
* Updated deployment scripts, compose files, and reverse-proxy templates to target the combined server; added example configs and getting-started updates.
With this change we should be able to collect and expose the following histograms:
* `management.updatechannel.create.duration.ms` with `closed` boolean label
* `management.updatechannel.create.duration.micro` with `closed` boolean label
* `management.updatechannel.close.one.duration.ms`
* `management.updatechannel.close.one.duration.micro`
* `management.updatechannel.close.multiple.duration.ms`
* `management.updatechannel.close.multiple.duration.micro`
* `management.updatechannel.close.multiple.channels`
* `management.updatechannel.send.duration.ms` with `found` and `dropped` boolean labels
* `management.updatechannel.send.duration.micro` with `found` and `dropped` boolean labels
* `management.updatechannel.get.all.duration.ms`
* `management.updatechannel.get.all.duration.micro`
* `management.updatechannel.get.all.peers`
