feat(server): 敏感字段加密与脱敏（F25）

- 新增敏感字段加密服务（AES-256-GCM，FIELD_ENCRYPTION_KEY）
- users 详情返回银行卡/身份证脱敏字段；新增 /users/:id/sensitive 特权明文接口并写审计
- 权限新增 system.users_sensitive（hr/admin）
- 更新 env/README 与 v3 CSV 状态推进

server/src/services/crypto/index.js

@@ -0,0 +1,147 @@
+const crypto = require("node:crypto");
+
+const ENCRYPTION_VERSION_PREFIX = "v1:";
+const AES_ALGO = "aes-256-gcm";
+const IV_LENGTH_BYTES = 12;
+const TAG_LENGTH_BYTES = 16;
+
+function resolveFieldEncryptionKey(config) {
+  const raw = config?.fieldEncryptionKey;
+  if (!raw || typeof raw !== "string" || !raw.trim()) {
+    return null;
+  }
+
+  let key;
+  try {
+    key = Buffer.from(raw.trim(), "base64");
+  } catch {
+    return null;
+  }
+
+  if (key.length !== 32) {
+    return null;
+  }
+
+  return key;
+}
+
+function encryptString(plaintext, key) {
+  const input = typeof plaintext === "string" ? plaintext : "";
+  if (!input) {
+    return "";
+  }
+  if (!Buffer.isBuffer(key) || key.length !== 32) {
+    throw new Error("Invalid encryption key");
+  }
+
+  const iv = crypto.randomBytes(IV_LENGTH_BYTES);
+  const cipher = crypto.createCipheriv(AES_ALGO, key, iv);
+  const cipherText = Buffer.concat([cipher.update(input, "utf8"), cipher.final()]);
+  const tag = cipher.getAuthTag();
+
+  const payload = `${ENCRYPTION_VERSION_PREFIX}${iv.toString("base64url")}:${tag.toString(
+    "base64url",
+  )}:${cipherText.toString("base64url")}`;
+
+  return payload;
+}
+
+function decryptString(value, key) {
+  const input = typeof value === "string" ? value : "";
+  if (!input) {
+    return null;
+  }
+  if (!input.startsWith(ENCRYPTION_VERSION_PREFIX)) {
+    return null;
+  }
+  if (!Buffer.isBuffer(key) || key.length !== 32) {
+    throw new Error("Invalid encryption key");
+  }
+
+  const body = input.slice(ENCRYPTION_VERSION_PREFIX.length);
+  const parts = body.split(":");
+  if (parts.length !== 3) {
+    return null;
+  }
+
+  const [ivB64, tagB64, cipherB64] = parts;
+  const iv = Buffer.from(ivB64, "base64url");
+  const tag = Buffer.from(tagB64, "base64url");
+  const cipherText = Buffer.from(cipherB64, "base64url");
+
+  if (iv.length !== IV_LENGTH_BYTES || tag.length !== TAG_LENGTH_BYTES || !cipherText.length) {
+    return null;
+  }
+
+  const decipher = crypto.createDecipheriv(AES_ALGO, key, iv);
+  decipher.setAuthTag(tag);
+
+  const plain = Buffer.concat([decipher.update(cipherText), decipher.final()]).toString("utf8");
+  return plain;
+}
+
+function decryptStringSafe(config, encrypted, logger) {
+  const key = resolveFieldEncryptionKey(config);
+  if (!key) {
+    return null;
+  }
+
+  try {
+    return decryptString(encrypted, key);
+  } catch (error) {
+    logger?.warn?.({ err: error }, "Sensitive field decrypt failed");
+    return null;
+  }
+}
+
+function encryptStringOrThrow(config, plaintext) {
+  const key = resolveFieldEncryptionKey(config);
+  if (!key) {
+    throw new Error("Missing FIELD_ENCRYPTION_KEY");
+  }
+  return encryptString(plaintext, key);
+}
+
+function decryptStringOrThrow(config, encrypted) {
+  const key = resolveFieldEncryptionKey(config);
+  if (!key) {
+    throw new Error("Missing FIELD_ENCRYPTION_KEY");
+  }
+
+  return decryptString(encrypted, key);
+}
+
+function maskKeepEnds(value, options = {}) {
+  const input = typeof value === "string" ? value.trim() : "";
+  if (!input) {
+    return null;
+  }
+
+  const keepStart = Math.max(0, Number(options.keepStart ?? 0));
+  const keepEnd = Math.max(0, Number(options.keepEnd ?? 0));
+
+  if (input.length <= keepStart + keepEnd) {
+    return "*".repeat(input.length);
+  }
+
+  const start = keepStart ? input.slice(0, keepStart) : "";
+  const end = keepEnd ? input.slice(-keepEnd) : "";
+  return `${start}${"*".repeat(input.length - keepStart - keepEnd)}${end}`;
+}
+
+function maskBankAccount(account) {
+  return maskKeepEnds(account, { keepStart: 4, keepEnd: 4 });
+}
+
+function maskIdNumber(idNumber) {
+  return maskKeepEnds(idNumber, { keepStart: 6, keepEnd: 4 });
+}
+
+module.exports = {
+  decryptStringSafe,
+  decryptStringOrThrow,
+  encryptStringOrThrow,
+  maskBankAccount,
+  maskIdNumber,
+  resolveFieldEncryptionKey,
+};