Show per-disk usage for Proxmox-linked servers too, not just a total

The agent path showed a per-mount usage table; a Proxmox-linked server
only ever got a single "Disk (allocated)" figure, since that's all the
VM/LXC config alone can tell you -- it's the attached disk's declared
size, not how full it actually is inside the guest. Fix the actual gap
instead of just matching the display: fetch real usage where Proxmox
can see it.

adapter.getGuestDetail() gained a `disks` field (same {mount,
sizeBytes, usedBytes} shape the agent already reports, so the frontend
renders both identically):
- LXC: the host can read straight into the container's root
  filesystem, no agent needed -- status/current's disk/maxdisk fields
  are real usage, not just allocation.
- QEMU: the hypervisor can't see inside a virtual disk at all without
  help, so this calls the QEMU guest agent's get-fsinfo command (same
  "gracefully degrade if the agent's missing/older" tolerance already
  used for its IP-address lookup, and independent of it -- one
  command failing doesn't take out the other). Pseudo-filesystems
  (tmpfs, etc.) are filtered out by checking for a non-empty backing
  `disk` array, the common convention for this endpoint.

Extracted the disks-table JSX (previously only in the agent branch)
into a shared DisksTable component and used it in both branches, and
added a note explaining an empty result when a running QEMU VM's
guest agent doesn't support get-fsinfo (an older agent version).

Verified against a mock Proxmox API over real TLS: an LXC's root
usage, a QEMU VM's real fsinfo mounts (with the disk-less tmpfs entry
correctly filtered), and a QEMU VM whose get-fsinfo fails outright --
confirming that degrades to an empty disks list without throwing and
without affecting the separate network-get-interfaces result.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -49,8 +49,11 @@ All modules from the original plan are built:
   clicking a server opens its detail page with CPU/RAM/disk status, IP
   addresses, matching DNS names (looked up from the DNS module's cache), and
   its scheduled tasks — live hardware from Proxmox for VM/LXC-backed
-  servers, or from the agent's own hardware report for everything else.
-  Proxmox-linked servers also get start/stop/restart buttons right on the
+  servers, or from the agent's own hardware report for everything else,
+  both showing the same per-disk usage breakdown (an LXC's root filesystem
+  read straight from the host; a QEMU VM's actual mounts via its guest
+  agent, alongside the allocated size Proxmox already knew about without
+  one). Proxmox-linked servers also get start/stop/restart buttons right on the
   detail page. The detail page also has an **Admin Links** section
   (operator/admin to add/edit/remove) for bookmarking that server's own
   admin UIs — Dockge, Webmin, Cockpit, Portainer, or anything else reachable