feat(traces): drill from General-service metric charts to native traces

[wu-sheng]

Why

Requested in discussion #13934: when a service / API's latency or error rate looks abnormal on a trend chart, operators want to click the spike and land on the matching traces instead of hand-building a trace filter. Only latency and success/error metrics have a natural trace criterion, so the drill is scoped to those.

What

• Metric → native-trace drill on the General service layer. Drill-capable line widgets — Avg Response Time, Response Time Percentile, Error Rate, Apdex, Success Rate, MQ consume latency, across the Service / Instance / Endpoint scopes — carry a traces flag in their header and their datapoints are clickable. Clicking a point pins a small "View slow/error traces →" popover; the link opens the native Traces list in a new browser tab, pre-filtered to that service (and the selected instance / endpoint) and centered on the clicked bucket's window.
  • Latency widget → slowest-first (queryOrder=BY_DURATION) with minTraceDuration = the clicked value.
  • Error / success-rate widget → traceState=ERROR.
  • Throughput / resource widgets offer no drill.
• Config, not inference. A new optional traceDrill: { mode: 'latency' | 'error' } field on DashboardWidget, authored in the widget editor next to the MQE and enabled only when the layer's native Traces component is on (disabled with a notice otherwise). The bundled General service template stamps the ten eligible widgets; it also works on custom General-service dashboards.
• Fix: the dashboard "Reading data…" gate hung on Back-from-Traces — a warm vue-query cache repopulates synchronously on remount with no change event, so the freshness watch now runs immediately at mount.
• Fix: the drill popover no longer stacks under the chart hover tooltip.
• Remove: the deprecated layerScope widget option. It emitted OAP's scope: All entity (deprecated in the query-protocol since 9.4.0) and no bundled dashboard used it; legacy stored dashboards degrade to normal service scope.

No backend / query-protocol change — minTraceDuration + traceState already exist on the trace query.

Validation

• type-check, build-ui, build-bff, license:check (0 invalid), lint, test:unit (BFF 172, UI 133) all green.
• New UI strings translated across all 8 locales (en source + zh-CN / es / pt / ja / ko / de / fr); completeness verified.
• Rendered against the demo OAP in the dev stack: the traces flag renders on the eligible General-service widgets, a datapoint click opens the pre-filtered Traces tab, and the popover/tooltip no longer overlap.
• Still worth a focused check on a live OAP before release: the instance/endpoint name → OAP id resolution on the Instance/Endpoint scopes (endpoint id is a serviceId+name composite), and the second-precision centered window.