add prometheus instrumentation

README.md

@@ -33,6 +33,18 @@ Run `swag init --exclude "pkg.mod,pkg.build,pkg.tools" -o server/router/docs`
 - Daily summaries aggregate the hourly snapshots for the day; monthly summaries aggregate daily summaries for the month.
 - Snapshots are registered in `snapshot_registry` so regeneration via `/api/snapshots/aggregate` can locate the correct tables (fallback scanning is also supported).
 - Reports (XLSX with totals/charts) are generated automatically after hourly, daily, and monthly jobs and written to a reports directory.
+- Prometheus metrics are exposed at `/metrics`:
+  - Snapshots/aggregations: `vctp_hourly_snapshots_total`, `vctp_hourly_snapshots_failed_total`, `vctp_hourly_snapshot_last_unix`, `vctp_hourly_snapshot_last_rows`, `vctp_daily_aggregations_total`, `vctp_daily_aggregations_failed_total`, `vctp_daily_aggregation_duration_seconds`, `vctp_monthly_aggregations_total`, `vctp_monthly_aggregations_failed_total`, `vctp_monthly_aggregation_duration_seconds`, `vctp_reports_available`
+  - vCenter health/perf: `vctp_vcenter_connect_failures_total{vcenter}`, `vctp_vcenter_snapshot_duration_seconds{vcenter}`, `vctp_vcenter_inventory_size{vcenter}`
+
+#### RPM Layout (summary)
+The RPM installs the service and defaults under `/usr/bin`, config under `/etc/dtms`, and data under `/var/lib/vctp`:
+- Binary: `/usr/bin/vctp-linux-amd64`
+- Systemd unit: `/etc/systemd/system/vctp.service`
+- Defaults/env: `/etc/dtms/vctp.yml` (override with `-settings`), `/etc/default/vctp` (environment)
+- TLS cert/key: `/etc/dtms/vctp.crt` and `/etc/dtms/vctp.key` (generated if absent)
+- Data: SQLite DB and reports default to `/var/lib/vctp` (reports under `/var/lib/vctp/reports`)
+- Scripts: preinstall/postinstall handle directory creation and permissions.
 
 #### Settings File
 Configuration now lives in the YAML settings file. By default the service reads