P7: restore agent node type, agent heartbeat expiry, build-version injection, remove log/history/xray-metrics modules, optional sub port

- nodes: port node-type (traditional/agent) picker back from web-src into
  the embedded frontend; backend annotates NodeView.nodeType from
  agent_nodes bindings; fix agent-node update path (skip reachability
  probe and apiToken requirement for agent-managed nodes); restore i18n
  keys in all 13 locales; install command now uses the Gitea mirror
- jobs: expire agent-bound nodes whose agent_nodes.last_seen is older
  than max(3x heartbeat interval, 120s) = 180s; last_seen=0 (never
  registered) is left untouched; transitions reuse UpdateHeartbeat +
  node event broadcast
- config: GetBaseVersion honors ldflags-injected buildVersion; release
  builds inject 3.7.0-agent.1 so the panel no longer reports a phantom
  update against the Gitea release tag
- logger/server: remove the three log viewers (panel/xray/amneziawg),
  their API endpoints and the 10240-entry in-memory log buffer; file
  logging via lumberjack unchanged; tests assert via a new optional
  logger hook instead of the removed buffer
- server: remove system history and xray metrics modules end to end
  (endpoints, sampling appends in RefreshStatus, per-minute persist
  cron, gob snapshot/restore, XrayMetricsService); realtime status and
  per-node history are untouched
- settings: subPort may be 0/unset - subscription links are generated
  without a port while the subscription service keeps binding the
  default 2096; the settings form declares the cleared state via
  onNumber's new onClear option instead of snapping back to 1

internal/web/service/metric_history_test.go

@@ -144,21 +144,6 @@ func TestAggregateLongSpanUsesCoarseTier(t *testing.T) {
 	}
 }
 
-func TestSnapshotRestoreRoundTrip(t *testing.T) {
-	h := newMetricHistory()
-	now := time.Now().Unix()
-	for i := range int64(10) {
-		h.append("cpu", time.Unix(now-(9-i)*2, 0), float64(i))
-	}
-
-	h2 := newMetricHistory()
-	h2.restore(h.snapshot())
-
-	if out := h2.aggregate("cpu", 2, 60); len(out) == 0 {
-		t.Fatalf("expected restored series to aggregate")
-	}
-}
-
 func TestAggregateMissingMetricIsEmpty(t *testing.T) {
 	h := newMetricHistory()
 	if out := h.aggregate("nope", 2, 60); len(out) != 0 {