refactor: apply new utilities and constants across codebase

P0 fixes:
- KV Cache migration: security.ts now delegates to kv-cache.ts (74% code reduction)
- Environment validation: index.ts validates env on first request
- Type safety: optimistic-lock.ts removes `as any` with proper interface

P1 improvements:
- Constants applied to deposit-agent.ts (TRANSACTION_STATUS, TRANSACTION_TYPE)
- Constants applied to callback-handler.ts (CALLBACK_PREFIXES)
- Constants applied to domain-tool.ts (MESSAGE_MARKERS)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/constants/index.ts

@@ -48,12 +48,17 @@ export const KEYBOARD_TYPES = {
  *
  * Format: prefix:action:params
  * Examples:
- *   - domain_reg:confirm:example.com:15000
- *   - server_order:confirm:order_123
+ *   - domain_reg:example.com:15000
+ *   - server_order:userId:index
+ *   - server_cancel:userId
  */
 export const CALLBACK_PREFIXES = {
-  DOMAIN_REGISTER_CONFIRM: 'confirm_domain_register',
-  DOMAIN_REGISTER_CANCEL: 'cancel_domain_register',
+  DOMAIN_REGISTER: 'domain_reg',
+  DOMAIN_CANCEL: 'domain_cancel',
+  SERVER_ORDER: 'server_order',
+  SERVER_CANCEL: 'server_cancel',
+  CONFIRM_DOMAIN_REGISTER: 'confirm_domain_register',
+  CANCEL_DOMAIN_REGISTER: 'cancel_domain_register',
   SERVER_ORDER_CONFIRM: 'confirm_server_order',
   SERVER_ORDER_CANCEL: 'cancel_server_order',
   DELETE_CONFIRM: 'confirm_delete',