fix(verification): 验证码提取保留原文大小写

[devin-ai-integration]

Pull request type / PR 类型

• Bugfix / Bug 修复

What is the current behavior? / 当前行为是什么？

验证码提取收口时对提取结果强制 .upper()，导致含字母的验证码大小写被篡改。例如邮件正文验证码为 ab12cd，接口返回 AB12CD（verification_code 与 formatted 都被改）。

链路：get_verification_result → _run_generic_verification_extract → extract_verification_info_with_options → enhance_verification_with_ai_fallback。

Issue Number / Issue 编号: N/A

What is the new behavior? / 新行为是什么？

outlook_web/services/verification_extractor.py 移除验证码取值处的强制大写，保留邮件原文大小写：

• _smart_extract_code_by_keywords：return value.upper() → return value
• _fallback_extract_code：candidates.append(value.upper()) → append(value)
• 历史函数 smart_extract_verification_code：return match.upper() → return match
• 历史函数 fallback_extract_verification_code：filtered.append(match.upper()) → append(match)（过滤判断仍基于原值，逻辑不变）
• AI 回退 enhance_verification_with_ai_fallback：result["verification_code"] = ai_code.upper() → = ai_code

formatted 由 verification_code 重算，因此同步保持原大小写。

仅改大小写取值，不改动匹配范围/置信度/互斥等其它逻辑（其余 .upper() 如 HTTP method、错误码分类均保持不变）。

补充回归测试：

• tests/test_verification_extractor.py：规则分支小写 / 大小写混合（ab12cd、Ab12Cd）保持原样，且 formatted 一致
• tests/test_ai_fallback_trigger_condition.py：AI 回退返回 cbdfdb 时保持小写

本地验证：新增及相关用例全部通过；black / isort / flake8(E9,F63,F7,F82) 均通过。

Release notes / 发布日志

已在 CHANGELOG.md 的 [Unreleased] / 修复 中记录：验证码提取保留原文大小写。

Other information / 其他信息

无。

Link to Devin session: https://app.devin.ai/sessions/f4c5628e21d4407e9b9133c97851be53
Requested by: @ZeroPointSix

[devin-ai-integration]

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[ZeroPointSix]

Migration note: the applicable changes from this PR have been ported into #112, targeting the #109 SPA migration branch.

#112 includes the registration mail pool API/docs/backend pieces and related validation. Full validation details are in the new PR body.

[ZeroPointSix]

已将本 PR 纳入 issue #115 的旧前端紧急版本专用合并分支：#117 #117

该分支仅汇总旧前端优先修复，目前包含 #67/#103/#108，明确不包含 #109/#110/#111/#112 新前端/SPA 线。远端沙箱验证已通过：focused regression 138 tests OK，full python -m unittest discover -s tests -v exit 0。