Add a "Sync from Proxmox" action to IP Addresses (IPAM)

Extends the Tailscale IPAM sync to Proxmox: pulls every VM/LXC's IP
address(es) across all enabled Proxmox integrations into the
inventory, reusing the same never-overwrite-a-manual-entry semantics.

Proxmox guests can have multiple NICs (each IP synced as its own
entry) and, for QEMU VMs, IP discovery depends on a responsive guest
agent — a VM with none simply contributes zero entries rather than
erroring, matching getGuestDetail()'s existing best-effort behavior.
listGuests() doesn't include IPs, so this fetches getGuestDetail() per
guest; acceptable for an explicit, user-triggered sync rather than a
background poll.

Extracted the shared "insert, update only if I own this row, else
skip and report" upsert logic (previously inline in the Tailscale sync
handler) into upsertSyncedEntry(), now used by both sync routes so the
core safety rule can't drift between them.

Verified end-to-end against a mock Proxmox server covering: an LXC
with two NICs (both synced), a QEMU VM with a responsive guest agent,
a QEMU VM with no agent (zero entries, no error), a manual-entry
collision (skipped and reported, never overwritten), and idempotent
re-sync (add -> update on the second run).

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

README.md

@@ -19,9 +19,10 @@ All modules from the original plan are built:
 - Authentik OIDC login, roles (first user to sign in becomes admin), audit log
 - **Secrets** — expiry tracking for API tokens/certs/passwords
 - **IP Addresses (IPAM)** — inventory of IPs across vendors/locations,
-  with a "Sync from Tailscale" action to pull in tailnet device IPs
-  (never overwrites a manually-entered IP), and each entry now shows
-  its matching DNS record(s) from the DNS module's cache
+  with "Sync from Tailscale" and "Sync from Proxmox" actions to pull in
+  tailnet device IPs and VM/LXC IPs (never overwrites a
+  manually-entered IP), and each entry now shows its matching DNS
+  record(s) from the DNS module's cache
 - **DNS** — zone/record management across Cloudflare, Loopia, Pi-hole, Azure
   DNS, cPanel, and Technitium; providers are configured in-app (not via env
   vars) and their credentials are encrypted at rest