V2.0.1: listen override fix, sing-box core fetch, probe settings page + fast report, spx removal, core mem env

- 0: sing-box gen overrides fragment listen/port from the inbound row
  (empty listen -> "::"), Update/Add recompute the stored fragment;
  non-loopback E2E against the real core binary.
- 1: agent fetches the sing-box core from the Gitea release when
  missing, self-checks it, and only then latches the switch.
- 2: node list shows the sing-box core version (heartbeat field,
  persisted on the node row), xray version as fallback.
- 3: public-page fallback returns 404 to anonymous visitors when the
  page is disabled.
- 4: settings restart hint bar removed, dead i18n keys cleaned.
- 5: two PUT calls missing JSON headers fixed (audit: only those two),
  batch probe-task creation endpoint + UI.
- 6: cf-probe retirement card and coverage pipeline removed.
- 7: generated vless links no longer carry spx (panel export + sub);
  parser still accepts spx; golden fixtures updated.
- probe batch: dedicated probe settings tab (public-page settings,
  tasks, per-node meta), retention_days editable, per-node traffic
  calibration + stat-interface pinning, runtime metrics split into a
  lightweight fast report (default 3s, 1-60s adjustable).
- 8: sing-box core processes start with GOMEMLIMIT=32MiB, GOGC=50.
- 9: dead /getTwoFactorEnable docs entries removed (frontend call and
  contract entry already gone at base; verified by grep).

internal/web/service/probe_public.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"net"
 	"sort"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -56,6 +57,25 @@ func setProbeSetting(key, value string) error {
 	return db.Save(&row).Error
 }
 
+// ProbeFastIntervalSec is the agent fast-report cadence in seconds
+// (V2.0.1 probe batch): runtime metrics ride a lightweight report at
+// this interval instead of the 60 s heartbeat. Default 3, operator
+// range 1–60 (setting key probe_fast_interval).
+func ProbeFastIntervalSec() int {
+	v, ok := probeSetting("probe_fast_interval")
+	if !ok {
+		return 3
+	}
+	n, err := strconv.Atoi(strings.TrimSpace(v))
+	if err != nil || n < 1 {
+		return 3
+	}
+	if n > 60 {
+		return 60
+	}
+	return n
+}
+
 // ProbePublicPageEnabled reports the public-page master switch. Per
 // the item-7 scope decision the page ships OFF until the operator
 // turns it on (setting public_page = "on"); the hub's own default is