feat: support PBS hosts and remote PBS monitoring

docs/pbs.md

@@ -0,0 +1,66 @@
+# Proxmox Backup Server support
+
+ProxMenux detects PBS from the installed **proxmox-backup-server** package.
+Installing proxmox-backup-client on PVE or another Debian system does not turn
+that host into PBS. Supported maintenance platforms are PBS 3/Debian 12 and
+PBS 4/Debian 13; PVE 8/9 detection remains separate. If both server products
+are co-installed, PVE takes precedence.
+
+## On a PBS host
+
+The main CLI opens a PBS menu with package/version information, datastores,
+recent tasks, the existing system-utility installer, settings and a PBS package
+update. Utility installation preserves the operator's APT sources instead of
+trying to find a PVE version or enabling PVE/Ceph repositories. Configure a
+working subscription or no-subscription PBS repository in PBS itself if APT
+reports an error.
+
+The update refreshes configured indexes, displays the simulated full-upgrade
+plan and requires confirmation before applying it. It does not run PVE repository
+cleanup, major-version migration, kernel cleanup or guest scripts. The automatic
+and customizable PVE post-install entry points reject PBS before adjustments.
+
+Monitor opens a PBS dashboard with CPU, RAM, uptime, local PBS status,
+datastores, recent tasks and maintenance schedules, plus logs, terminal and
+Monitor authentication/HTTPS settings. PVE guest prewarmers, firewall controls
+and guest-storage checks are not part of this dashboard. Health checks monitor
+proxmox-backup and proxmox-backup-proxy rather than reporting absent PVE daemons.
+Monitor can reuse the native PBS proxy.pem/proxy.key pair, including renewal.
+
+Local data is read with proxmox-backup-manager JSON commands. Datastore capacity
+is filesystem capacity, not the logical sum of backups; datastores sharing one
+filesystem can show the same capacity. An unmounted removable datastore or a
+failed check has unknown capacity, not zero/free space.
+
+## Monitor a remote PBS from PVE
+
+Open **Backup → Proxmox Backup Server → Manage PBS connections**. Enable local
+Monitor authentication first, then add a named HTTPS endpoint (for example
+https://pbs.example:8007), a dedicated API token ID (`user@pbs!monitor`) and its
+secret. Give both the user and token the PBS **Audit** role on `/`, with
+propagation, to view system tasks and datastore status. Token ACLs cannot exceed
+the user's effective permissions. A restricted token may show only its permitted
+data; denied sections are displayed as unavailable.
+
+Use a CA-trusted certificate or copy the certificate's SHA256 fingerprint from
+the PBS console/a trusted channel. With a pin, Monitor checks the peer certificate
+before sending the token. With no pin, the normal system CA and hostname checks
+apply. Connections go directly to the configured HTTPS endpoint and do not follow
+redirects. A reverse-proxy prefix is supported; omit the port for HTTPS 443 or
+include the native PBS port explicitly.
+
+Saving tests an authenticated datastore-status endpoint. Secrets are stored
+atomically with mode 0600 in `~/.config/proxmenux-monitor/pbs_servers.json`, never
+returned by the API, and retained when the edit form's secret is left empty.
+Connection changes require full administrator access; read-only Monitor API tokens
+can read monitoring data but cannot change connections. Removing a connection
+removes its saved credentials only. Monitoring does not start prune, garbage
+collection, verification or sync jobs and does not modify PBS backups.
+
+Status is cached for 15 seconds and the panel refreshes every 30 seconds. Task or
+schedule permission failures are shown independently, without hiding successful
+datastore data or presenting failed queries as empty healthy results.
+
+References: [PBS command syntax](https://pbs.proxmox.com/docs/command-syntax.html),
+[PBS API](https://pbs.proxmox.com/docs/api-viewer/index.html),
+[PBS users, tokens and ACLs](https://pbs.proxmox.com/docs/user-management.html).