feat(admin): time-series trend charts on the metrics tabs (0.87.0)

Turn the dormant timing data in crawl_metrics / page_analysis into "is it
healthy over time" views. New bucketed series queries (GROUP BY date_trunc,
hour|day via a closed Bucket enum so the unit can't be attacker-controlled)
behind GET /v1/admin/{crawler,analysis}/metrics/series, with a shared
SeriesParams/resolve_bucket helper (bad bucket → 400) and migration 0030
indexing page_analysis(analyzed_at) for the analysis scan.

Frontend: a dependency-free SVG TrendChart (line+area, null buckets render as
gaps, empty-state, role=img) embedded above the per-op tables in Crawler and
Analysis → Metrics, driven by each panel's existing window selector with
AbortController-cancelled fetches. A buildSeries() util fills the continuous
bucket axis (throughput 0 for empty buckets, success/duration null) — unit
tested alongside the chart and the series API client.

Closes the Phase-1 observability set (audit log · health checks · trends).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/repo/crawl_metrics.rs

@@ -8,7 +8,24 @@ use chrono::{DateTime, Utc};
 use sqlx::PgPool;
 use uuid::Uuid;
 
-use crate::domain::crawl_metrics::{OpRow, OpSummary};
+use crate::domain::crawl_metrics::{MetricsBucket, OpRow, OpSummary};
+
+/// Time-bucket granularity for trend series. A closed enum (not a free
+/// string) so the `date_trunc` unit can never be attacker-controlled.
+#[derive(Debug, Clone, Copy)]
+pub enum Bucket {
+    Hour,
+    Day,
+}
+
+impl Bucket {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Bucket::Hour => "hour",
+            Bucket::Day => "day",
+        }
+    }
+}
 
 /// Operation kinds, kept as consts so call sites and the CHECK constraint
 /// don't drift from a free-typed literal.
@@ -75,6 +92,34 @@ pub async fn summary(
     .await
 }
 
+/// Bucketed throughput/success/duration series over an optional window.
+/// Plain `GROUP BY date_trunc(...)` — empty intervals are absent and the
+/// client fills the continuous axis. Uses `crawl_metrics_time_idx`.
+pub async fn series(
+    pool: &PgPool,
+    bucket: Bucket,
+    since: Option<DateTime<Utc>>,
+) -> sqlx::Result<Vec<MetricsBucket>> {
+    sqlx::query_as::<_, MetricsBucket>(
+        r#"
+        SELECT
+            date_trunc($1, finished_at)                  AS t,
+            COUNT(*)                                     AS n,
+            COUNT(*) FILTER (WHERE outcome = 'ok')       AS ok,
+            COUNT(*) FILTER (WHERE outcome = 'failed')   AS failed,
+            AVG(duration_ms)::float8                     AS avg_ms
+          FROM crawl_metrics
+         WHERE ($2::timestamptz IS NULL OR finished_at >= $2)
+         GROUP BY t
+         ORDER BY t
+        "#,
+    )
+    .bind(bucket.as_str())
+    .bind(since)
+    .fetch_all(pool)
+    .await
+}
+
 /// Filters for [`list_ops`]. `None`/empty widens the scope.
 #[derive(Debug, Default, Clone)]
 pub struct OpFilter<'a> {

backend/src/repo/page_analysis.rs

@@ -495,6 +495,39 @@ pub async fn analysis_metrics(
     Ok(AnalysisMetrics { n, ok, failed, avg_ms, by_model })
 }
 
+/// Bucketed analysis throughput/success/duration series over an optional
+/// window, for the Analysis-tab trend charts. `ok`/`failed` follow the
+/// `done`/`failed` statuses; mean duration is over completed pages only.
+/// Empty intervals are absent (client fills the axis). The
+/// `page_analysis_analyzed_at_idx` (migration 0030) backs the scan.
+pub async fn analysis_series(
+    pool: &PgPool,
+    bucket: crate::repo::crawl_metrics::Bucket,
+    since: Option<DateTime<Utc>>,
+) -> AppResult<Vec<crate::domain::crawl_metrics::MetricsBucket>> {
+    let rows = sqlx::query_as::<_, crate::domain::crawl_metrics::MetricsBucket>(
+        r#"
+        SELECT
+            date_trunc($1, analyzed_at)                          AS t,
+            COUNT(*)                                             AS n,
+            COUNT(*) FILTER (WHERE status = 'done')              AS ok,
+            COUNT(*) FILTER (WHERE status = 'failed')            AS failed,
+            AVG(duration_ms) FILTER (WHERE status = 'done')::float8 AS avg_ms
+          FROM page_analysis
+         WHERE status <> 'pending'
+           AND analyzed_at IS NOT NULL
+           AND ($2::timestamptz IS NULL OR analyzed_at >= $2)
+         GROUP BY t
+         ORDER BY t
+        "#,
+    )
+    .bind(bucket.as_str())
+    .bind(since)
+    .fetch_all(pool)
+    .await?;
+    Ok(rows)
+}
+
 /// Persist a completed analysis for a page, replacing any previous result.
 ///
 /// The model's free-form `kind` / `content_type` strings are mapped onto