Replace state blob with resource-oriented API endpoints

Split /api/v1/state into dedicated resource endpoints:
- /api/v1/operator, /api/v1/central-domain
- /api/v1/ddns/config, /api/v1/dns/settings
- /api/v1/dhcp/config (moved from /dnsmasq/dhcp/)
- /api/v1/nftables/config, /api/v1/haproxy/routes

Each page now talks to its own resource instead of deep-merging
a blob. Removes useConfig hook, CentralState type, and legacy
config methods.

web/src/services/api/networking.ts

@@ -144,15 +144,15 @@ export interface DhcpStaticLease {
 
 export const dhcpApi = {
   async getLeases(): Promise<{ leases: DhcpLease[] }> {
-    return apiClient.get('/api/v1/dnsmasq/dhcp/leases');
+    return apiClient.get('/api/v1/dhcp/leases');
   },
 
   async addStatic(lease: DhcpStaticLease): Promise<{ message: string }> {
-    return apiClient.post('/api/v1/dnsmasq/dhcp/static', lease);
+    return apiClient.post('/api/v1/dhcp/static', lease);
   },
 
   async deleteStatic(mac: string): Promise<{ message: string }> {
-    return apiClient.delete(`/api/v1/dnsmasq/dhcp/static/${encodeURIComponent(mac)}`);
+    return apiClient.delete(`/api/v1/dhcp/static/${encodeURIComponent(mac)}`);
   },
 };