fix(ui): correct SNMP protocol values and simplify add-device flow

- Add missing fields to SNMPProfileResponse (sys_object_id, vendor, category, tenant_id)
- Fix security level values to snake_case (no_auth_no_priv, auth_no_priv, auth_priv) matching backend
- Fix auth protocols to SHA256/SHA384/SHA512 (was MD5/SHA/SHA256)
- Fix privacy protocols to AES128/AES256 (was DES/AES/AES256)
- Apply same protocol fixes to ProfileTestPanel
- Fix BulkAddForm to show both v2c and v3 credential profiles (was hardcoded to v2c)
- Simplify SNMP tab in AddDeviceForm to IP + credential profile + discover-and-add button
- Show guidance link when no SNMP credential profiles exist

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/lib/api.ts

@@ -551,6 +551,10 @@ export interface SNMPProfileResponse {
   description: string | null
   is_system: boolean
   profile_data: Record<string, unknown> | null
+  sys_object_id: string | null
+  vendor: string | null
+  category: string | null
+  tenant_id: string | null
   device_count: number
   created_at: string
   updated_at: string