fix(observability): merge rollup+raw hourly trends and backfill history

Prefer capacity/openresty rollups only when they cover the 24h window;
otherwise merge per hour so raw fills pre-MV gaps and rollup wins on
overlap. Add a one-time ANTI JOIN backfill migration for the last 30 days.

internal/db/migrator/goose/clickhouse/202607100003_backfill_metric_openresty_hourly.sql

@@ -0,0 +1,66 @@
+-- +goose Up
+-- One-time historical backfill for hours not yet present in rollup tables.
+-- MV only ingests rows after creation; without this, 24h charts rely on raw merge forever.
+-- ANTI JOIN avoids double-counting hours already filled by the live MV.
+
+INSERT INTO of_node_metric_capacity_hourly
+SELECT
+    s.node_id,
+    toStartOfHour(s.captured_at) AS hour,
+    sum(s.cpu_usage_percent) AS cpu_usage_sum,
+    toUInt64(count()) AS cpu_usage_count,
+    sum(if(s.memory_total_bytes > 0, (s.memory_used_bytes * 100.0) / s.memory_total_bytes, 0)) AS memory_usage_sum,
+    toUInt64(countIf(s.memory_total_bytes > 0)) AS memory_usage_count,
+    min(s.network_rx_bytes) AS network_rx_min,
+    max(s.network_rx_bytes) AS network_rx_max,
+    min(s.network_tx_bytes) AS network_tx_min,
+    max(s.network_tx_bytes) AS network_tx_max,
+    min(s.disk_read_bytes) AS disk_read_min,
+    max(s.disk_read_bytes) AS disk_read_max,
+    min(s.disk_write_bytes) AS disk_write_min,
+    max(s.disk_write_bytes) AS disk_write_max
+FROM of_node_metric_snapshots AS s
+ANTI JOIN
+(
+    SELECT
+        node_id,
+        hour
+    FROM of_node_metric_capacity_hourly
+    GROUP BY
+        node_id,
+        hour
+) AS existing
+ON s.node_id = existing.node_id AND toStartOfHour(s.captured_at) = existing.hour
+WHERE s.captured_at >= now() - INTERVAL 30 DAY
+GROUP BY
+    s.node_id,
+    hour;
+
+INSERT INTO of_node_openresty_hourly
+SELECT
+    s.node_id,
+    toStartOfHour(s.captured_at) AS hour,
+    min(s.openresty_rx_bytes) AS openresty_rx_min,
+    max(s.openresty_rx_bytes) AS openresty_rx_max,
+    min(s.openresty_tx_bytes) AS openresty_tx_min,
+    max(s.openresty_tx_bytes) AS openresty_tx_max
+FROM of_node_obs_openresty AS s
+ANTI JOIN
+(
+    SELECT
+        node_id,
+        hour
+    FROM of_node_openresty_hourly
+    GROUP BY
+        node_id,
+        hour
+) AS existing
+ON s.node_id = existing.node_id AND toStartOfHour(s.captured_at) = existing.hour
+WHERE s.captured_at >= now() - INTERVAL 30 DAY
+GROUP BY
+    s.node_id,
+    hour;
+
+-- +goose Down
+-- Backfill is additive; down does not remove historical rollup rows (TTL still applies).
+SELECT 1;