feat: IPAM improvements - server/node subnet binding, theme color fixes

- IPAM link-allocations: filter networks by proxmox_server_id and proxmox_node
  to prevent cross-server/cross-node IP assignment
- IPAM link-allocations: add manual server+network selection modal before linking
- IPAM add-network forms: add Proxmox server and node selectors with dynamic
  cluster-info loading (ipam_dashboard.html, ipam_networks.html)
- models.py / schemas.py: add proxmox_node field to IPAMNetwork
- migrations: migration #16 adds proxmox_node column to ipam_networks table
- Theme fixes: replace all hardcoded rgba/color:#fff/color:white with CSS vars
  across base.html, virtual_machines.html, instance_detail.html,
  os_templates.html, proxmox_vms.html, ipam_network_detail.html,
  ipam_allocations.html
- i18n: add proxmox_node, node selector, link-allocations modal keys (ru/en)
- Version bump: 1.0.4 -> 1.0.5

backend/app/i18n.py

@@ -1710,6 +1710,26 @@ class I18nService:
             "ru": "Proxmox Bridge",
             "en": "Proxmox Bridge"
         },
+        "proxmox_node": {
+            "ru": "Нода Proxmox",
+            "en": "Proxmox Node"
+        },
+        "proxmox_node_hint": {
+            "ru": "Нода внутри кластера, к которой привязана сеть. Привязка будет учтена при поиске IP.",
+            "en": "Cluster node the network is associated with. Used for IP matching."
+        },
+        "all_nodes": {
+            "ru": "— Все ноды —",
+            "en": "— All nodes —"
+        },
+        "select_node": {
+            "ru": "— Выберите ноду —",
+            "en": "— Select node —"
+        },
+        "loading_nodes": {
+            "ru": "Загрузка нод...",
+            "en": "Loading nodes..."
+        },
         "proxmox_server": {
             "ru": "Proxmox сервер",
             "en": "Proxmox Server"
@@ -3606,6 +3626,26 @@ class I18nService:
             "ru": "Привязать все несвязанные адреса к соответствующим VM по имени?",
             "en": "Link all unlinked allocations to matching VMs by name?"
         },
+        "link_allocations_title": {
+            "ru": "Привязать IP к VM",
+            "en": "Link IPs to VMs"
+        },
+        "link_scope_hint": {
+            "ru": "Выберите сервер (ноду) и подсеть. Будут привязаны только ВМ выбранного сервера к выбранной подсети.",
+            "en": "Select a server (node) and subnet. Only VMs from the selected server will be linked to the selected subnet."
+        },
+        "select_server_for_link": {
+            "ru": "— Выберите сервер —",
+            "en": "— Select server —"
+        },
+        "select_network_first_server": {
+            "ru": "— Сначала выберите сервер —",
+            "en": "— Select server first —"
+        },
+        "no_networks_for_server": {
+            "ru": "Нет сетей для этого сервера",
+            "en": "No networks for this server"
+        },
         "cleaning": {
             "ru": "Очистка",
             "en": "Cleaning"