Unlink servers before deleting a Proxmox integration

servers.proxmox_integration_id was created (migration 0001) without an ON DELETE
rule, although schema.ts asks for "set null", so with foreign keys on, deleting
an integration that a server was linked to failed with a constraint error.
The delete route now clears the four proxmox_* columns on those servers first
and records how many it unlinked in the audit entry. schema.ts notes the gap.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

server/src/db/schema.ts

@@ -224,7 +224,9 @@ export const servers = sqliteTable("servers", {
   lastPortScan: text("last_port_scan"), // JSON string: summary of the most recent network scan from this app
   tags: text("tags"), // JSON string: string[] — free-form labels for grouping and filtering, normalized by services/serverTags
 
-  // Optional link to a Proxmox VM/LXC — set by an admin, not the agent.
+  // Optional link to a Proxmox VM/LXC — set by an admin, not the agent. The "set null" below is what this file asks for,
+  // but migration 0001 created the column without it, so the database itself has no ON DELETE rule here: deleting an
+  // integration clears these columns in routes/integrations.ts instead. (See DATABASE.md.)
   proxmoxIntegrationId: integer("proxmox_integration_id").references(() => integrations.id, {
     onDelete: "set null",
   }),