fix(channel-monitor-v2): default mode v1 and gentle adaptive backfill

Default channel_monitor_mode to v1 (opt-in V2) so upgrades keep active
probes; existing explicit v2 rows are left alone via ON CONFLICT DO NOTHING
plus migration checksum compatibility for already-applied 195.

V2 first-enable backfill no longer compresses ticks to 5s or uses 24h
chunks. Each tick does recent overlap plus at most one historical chunk
with depth-based ceilings (2h/4h/6h), adaptive grow/shrink, and failure
backoff. Error request_id dedup is bounded by a 90-minute lookback so
ops_error_logs is not scanned for full history.

Also align hide_throughput parse default with privacy-preserving public
runtime (missing key → true).

frontend/src/i18n/locales/en/admin/settings.ts

@@ -21,11 +21,11 @@ export default {
           enabled: 'Enable Channel Monitor',
           enabledHint: 'Disabling stops both the V1 scheduler and V2 aggregation; existing config and history are kept.',
           mode: 'Monitor mode',
-          modeHint: 'Only one implementation can be active: V2 never sends upstream probes; V1 probes configured monitors on a schedule.',
+          modeHint: 'Default is V1 (active probes). Switch to V2 only when you want passive aggregation; only one implementation can be active at a time.',
           modeV2: 'V2 passive monitoring',
           modeV1: 'V1 active probes',
-          modeV2Hint: 'Aggregates health metrics from real gateway traffic without upstream probe traffic.',
-          modeV1Hint: 'Runs scheduled upstream health checks for configured channel monitors (probe traffic).',
+          modeV2Hint: 'Opt-in: aggregates health metrics from real gateway traffic without upstream probe traffic. V1 probes stop while V2 is active.',
+          modeV1Hint: 'Default: runs scheduled upstream health checks for configured channel monitors (probe traffic).',
           defaultInterval: 'Default check interval (seconds)',
           defaultIntervalHint: 'V1 only: default interval for new monitors (overridable per monitor). Range 15 – 3600 seconds.',
           hideThroughput: 'Hide throughput rates from users (RPM / TPM)',

frontend/src/i18n/locales/zh/admin/settings.ts

@@ -21,11 +21,11 @@ export default {
           enabled: '启用渠道监控',
           enabledHint: '关闭后 V1 调度器与 V2 聚合均停止；已有配置与历史保留。',
           mode: '监控模式',
-          modeHint: '同一时间只能启用一种实现：V2 不产生上游探测流量；V1 会按配置的监控项主动探活。',
+          modeHint: '默认 V1（主动探测）。仅在需要被动聚合时切换到 V2；同一时间只能启用一种实现。',
           modeV2: 'V2 被动监控',
           modeV1: 'V1 主动探测',
-          modeV2Hint: '基于真实网关流量聚合健康指标，不向上游发送探活请求。',
-          modeV1Hint: '按配置的渠道监控项定时发起上游健康检查（产生探测流量）。',
+          modeV2Hint: '需主动选择：基于真实网关流量聚合健康指标，不向上游发送探活请求；启用期间 V1 探测停止。',
+          modeV1Hint: '默认模式：按配置的渠道监控项定时发起上游健康检查（产生探测流量）。',
           defaultInterval: '默认检测间隔（秒）',
           defaultIntervalHint: '仅 V1 模式使用：新建渠道监控时表单的默认值，可被单个渠道覆盖。范围 15 – 3600 秒。',
           hideThroughput: '对用户隐藏吞吐速率（RPM / TPM）',

frontend/src/utils/featureFlags.ts

@@ -160,11 +160,11 @@ export function isChannelMonitorRouteEnabled(): boolean {
 
 export type ChannelMonitorMode = 'v1' | 'v2'
 
-/** Exclusive channel-monitor implementation. Invalid/missing → v2. */
+/** Exclusive channel-monitor implementation. Invalid/missing → v1 (opt-in to v2). */
 export function getChannelMonitorMode(): ChannelMonitorMode {
   const appStore = useAppStore()
   const mode = appStore.cachedPublicSettings?.channel_monitor_mode
-  return mode === 'v1' ? 'v1' : 'v2'
+  return mode === 'v2' ? 'v2' : 'v1'
 }
 
 export function isChannelMonitorV1Mode(): boolean {

frontend/src/views/admin/SettingsView.vue

@@ -9516,7 +9516,7 @@ const form = reactive<SettingsForm>({
   account_quota_notify_emails: [] as NotifyEmailEntry[],
   // Channel Monitor feature switch
   channel_monitor_enabled: true,
-  channel_monitor_mode: 'v2' as 'v1' | 'v2',
+  channel_monitor_mode: 'v1' as 'v1' | 'v2',
   channel_monitor_default_interval_seconds: 60,
   channel_monitor_hide_throughput: false,
   // Available Channels feature switch
@@ -10516,7 +10516,7 @@ async function loadSettings() {
     form.login_agreement_mode =
       settings.login_agreement_mode === "checkbox" ? "checkbox" : "modal";
     form.channel_monitor_mode =
-      settings.channel_monitor_mode === "v1" ? "v1" : "v2";
+      settings.channel_monitor_mode === "v2" ? "v2" : "v1";
     form.channel_monitor_hide_throughput = Boolean(
       settings.channel_monitor_hide_throughput
     );