feat: add optimistic locking and improve type safety

- Implement optimistic locking for deposit balance updates
  - Prevent race conditions in concurrent deposit requests
  - Add automatic retry with exponential backoff (max 3 attempts)
  - Add version column to user_deposits table

- Improve type safety across codebase
  - Add explicit types for Namecheap API responses
  - Add typed function arguments (ManageDepositArgs, etc.)
  - Remove `any` types from deposit-agent and tool files

- Add reconciliation job for balance integrity verification
  - Compare user_deposits.balance vs SUM(confirmed transactions)
  - Alert admin on discrepancy detection

- Set up test environment with Vitest + Miniflare
  - Add 50+ test cases for deposit system
  - Add helper functions for test data creation

- Update documentation
  - Add migration guide for version columns
  - Document optimistic locking patterns

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

schema.sql

@@ -50,6 +50,7 @@ CREATE TABLE IF NOT EXISTS user_deposits (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
   user_id INTEGER NOT NULL UNIQUE,
   balance INTEGER NOT NULL DEFAULT 0,
+  version INTEGER NOT NULL DEFAULT 1,
   created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
   updated_at DATETIME DEFAULT CURRENT_TIMESTAMP,
   FOREIGN KEY (user_id) REFERENCES users(id)
@@ -89,6 +90,7 @@ CREATE TABLE IF NOT EXISTS deposit_transactions (
 CREATE INDEX IF NOT EXISTS idx_user_domains_user ON user_domains(user_id);
 CREATE INDEX IF NOT EXISTS idx_user_domains_domain ON user_domains(domain);
 CREATE INDEX IF NOT EXISTS idx_deposits_user ON user_deposits(user_id);
+CREATE INDEX IF NOT EXISTS idx_deposits_user_version ON user_deposits(user_id, version);
 CREATE INDEX IF NOT EXISTS idx_transactions_user ON deposit_transactions(user_id);
 CREATE INDEX IF NOT EXISTS idx_transactions_status ON deposit_transactions(status, created_at DESC);
 CREATE INDEX IF NOT EXISTS idx_transactions_prefix_pending ON deposit_transactions(status, type, depositor_name_prefix, amount, created_at) WHERE status = 'pending' AND type = 'deposit';