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/config/config_test.go

@@ -25,6 +25,34 @@ func TestGetPanelVersion(t *testing.T) {
 	}
 }
 
+func TestGetBaseVersionBuildVersionOverride(t *testing.T) {
+	orig := buildVersion
+	t.Cleanup(func() { buildVersion = orig })
+
+	// No injection (plain `go build`): the embedded version file wins.
+	buildVersion = ""
+	embedded := GetBaseVersion()
+	if embedded == "" {
+		t.Fatal("embedded version file must not be empty")
+	}
+
+	// Injected fork release version wins over the embedded file and flows
+	// into GetPanelVersion untouched (stable channel, no dev label).
+	buildVersion = "3.7.0-agent.1"
+	if got := GetBaseVersion(); got != "3.7.0-agent.1" {
+		t.Fatalf("injected build: GetBaseVersion = %q, want %q", got, "3.7.0-agent.1")
+	}
+	if got := GetPanelVersion(); got != "3.7.0-agent.1" {
+		t.Fatalf("injected build: GetPanelVersion = %q, want %q", got, "3.7.0-agent.1")
+	}
+
+	// Whitespace-only injection counts as unset.
+	buildVersion = "  "
+	if got := GetBaseVersion(); got != embedded {
+		t.Fatalf("blank injection: GetBaseVersion = %q, want embedded %q", got, embedded)
+	}
+}
+
 func TestGetPortOverride(t *testing.T) {
 	tests := []struct {
 		name       string