feat(db): HostMetric model for host-load sampling

Adds the per-minute snapshot table that backs the new admin host-load
chart above /admin/system-status. One row per minute, captured by the
pg-boss sampler in the next commit, with 7-day retention enforced
inside the worker so the table stays under a few thousand rows.

Schema mirrors what the chart needs:
  - load_avg_1/5/15 (DOUBLE PRECISION) — os.loadavg() output
  - mem_used_bytes / mem_total_bytes — derived from os.totalmem() and
    os.freemem(), kept as raw bytes so the API can compute either a
    percent or a MiB delta downstream
  - disk_read_bytes / disk_write_bytes — nullable cumulative byte
    counters from /proc/diskstats. NULL on macOS/Windows dev hosts;
    Linux production picks them up automatically. The API endpoint
    converts deltas to bytes-per-second between samples

Indexed by captured_at so the "last 2 hours" query stays index-only.

Migration 0032_host_metric. integration setup.ts adds host_metrics to
the truncate list so testcontainers stays clean across runs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

prisma/migrations/0032_host_metric/migration.sql

@@ -0,0 +1,31 @@
+-- v1.4.16 phase B3: per-minute host-load snapshot table.
+--
+-- The admin /system-status section now renders a 2-hour host-load chart
+-- above the existing facts grid (Marc: "über dem Systemstatus vielleicht
+-- nochmal so ein Graf der Auslastung des Hosts der letzten zwei Stunden").
+--
+-- A pg-boss `host-metric-sample` job inserts one row per minute carrying
+-- `os.loadavg()` (1/5/15-minute) + `os.totalmem() - os.freemem()` and,
+-- on Linux, a rolling cumulative byte counter from /proc/diskstats.
+-- Disk fields are nullable so non-Linux dev hosts keep working.
+--
+-- Retention: 7 days, enforced inside the sampler at the end of each
+-- tick. Indexed by `captured_at` so the API's `WHERE captured_at >=
+-- now() - 2h ORDER BY captured_at` query is index-only.
+
+CREATE TABLE "host_metrics" (
+  "id"               TEXT    NOT NULL,
+  "captured_at"      TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  "load_avg_1"       DOUBLE PRECISION NOT NULL,
+  "load_avg_5"       DOUBLE PRECISION NOT NULL,
+  "load_avg_15"      DOUBLE PRECISION NOT NULL,
+  "mem_used_bytes"   BIGINT NOT NULL,
+  "mem_total_bytes"  BIGINT NOT NULL,
+  "disk_read_bytes"  BIGINT,
+  "disk_write_bytes" BIGINT,
+
+  CONSTRAINT "host_metrics_pkey" PRIMARY KEY ("id")
+);
+
+CREATE INDEX "host_metrics_captured_at_idx"
+  ON "host_metrics" ("captured_at");

prisma/schema.prisma

@@ -757,3 +757,29 @@ model UserAchievement {
   @@index([userId])
   @@map("user_achievements")
 }
+
+// ─── Host Metrics (admin system-status host-load chart) ──────
+
+/// Per-minute snapshot of host-process load + memory captured by the
+/// pg-boss `host-metric-sample` job. Read by `/api/admin/host-metrics`
+/// to render the host-load trend above the system-status section.
+/// 7-day retention is enforced inside the sampler — we keep the table
+/// small enough that a single `findMany` over the last 2 hours stays
+/// well under 200 rows.
+model HostMetric {
+  id             String   @id @default(cuid())
+  capturedAt     DateTime @default(now()) @map("captured_at")
+  loadAvg1       Float    @map("load_avg_1")
+  loadAvg5       Float    @map("load_avg_5")
+  loadAvg15      Float    @map("load_avg_15")
+  memUsedBytes   BigInt   @map("mem_used_bytes")
+  memTotalBytes  BigInt   @map("mem_total_bytes")
+  // Optional rolling-window byte counters from /proc/diskstats. Null
+  // outside Linux (macOS dev machines, Windows). The API endpoint
+  // converts deltas into bytes-per-second client-side.
+  diskReadBytes  BigInt?  @map("disk_read_bytes")
+  diskWriteBytes BigInt?  @map("disk_write_bytes")
+
+  @@index([capturedAt])
+  @@map("host_metrics")
+}

tests/integration/setup.ts

@@ -43,6 +43,7 @@ export async function truncateAllTables(client: PrismaClient): Promise<void> {
     "data_backups",
     "devices",
     "feedback",
+    "host_metrics",
     "idempotency_keys",
     "integration_statuses",
     "measurements",