refactor(i18n): simplify wording by removing technical jargon

Apply PR NoFxAiOS#940 review feedback to z-dev-v2

## Change

Replace "十六进制字符" (hexadecimal characters) with "字符" (characters)

**Before:**
- `stage1Description: '请输入私钥的前 {length} 位十六进制字符'`
- `stage2Description: '请输入私钥的后 {length} 位十六进制字符'`

**After:**
- `stage1Description: '请输入私钥的前 {length} 位字符'`
- `stage2Description: '请输入私钥的后 {length} 位字符'`

## Rationale

As @xqliu suggested in PR NoFxAiOS#940 review:
"很多不学习计算机的不知道 16 进制跟 0x 对应"

- Technical term "十六进制" (hexadecimal) is too jargon-heavy for non-technical users
- The helpText already clearly explains the format: "不含 0x" / "含 0x 前缀"
- Simpler description improves UX for wider audience

## Related

- Syncs z-dev-v2 with PR NoFxAiOS#940 review feedback (commit b56afaa)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: the-dev-z

web/src/i18n/translations.ts

@@ -1613,8 +1613,8 @@ export const translations = {
     // Two-Stage Key Modal
     twoStageKey: {
       title: '两阶段私钥输入',
-      stage1Description: '请输入私钥的前 {length} 位十六进制字符',
-      stage2Description: '请输入私钥的后 {length} 位十六进制字符',
+      stage1Description: '请输入私钥的前 {length} 位字符',
+      stage2Description: '请输入私钥的后 {length} 位字符',
       stage1InputLabel: '第一部分',
       stage2InputLabel: '第二部分',
       characters: '位字符',