Fix macOS Git proxy discovery for system proxies

[JavisZhangSir-BYR]

What changed

This pull request makes GitDrop's external Git subprocess honor proxy settings on macOS.

Proxy resolution now follows this order:

1. GITDROP_HTTPS_PROXY
2. HTTPS_PROXY / https_proxy
3. ALL_PROXY / all_proxy
4. HTTP_PROXY / http_proxy
5. macOS system proxy returned by urllib.request.getproxies()

The implementation respects the system proxy bypass list for github.com. A proxy without credentials is passed through both standard proxy environment variables and a per-command configuration:

git -c http.proxy=<proxy> ...

Credentialed proxy URLs are passed only through the subprocess environment so their usernames and passwords never appear in process command-line arguments. This does not modify the user's global Git configuration.

Network failures now include a targeted proxy troubleshooting hint. Git output is defensively scrubbed of the GitHub token, raw proxy credentials, complete credentialed proxy URLs, and their URL-encoded forms.

Why

A macOS app launched from Finder does not normally inherit shell proxy environment variables. When Shadowrocket or another Fake-IP/TUN proxy is enabled, github.com may resolve to an address in 198.18.0.0/15. Without the system proxy, Git attempts to connect directly to that Fake-IP and fails with errors such as:

SSL_ERROR_SYSCALL
Connection reset by peer
Recv failure

Explicitly setting http.proxy=http://127.0.0.1:<port> makes clone and push work, confirming that the problem is missing proxy propagation rather than GitHub TLS, repository permissions, or authentication.

This is a separate network path from the GitHub API certificate and retry fix in #2.

Tests

Added 13 standard-library unittest cases covering:

• explicit GitDrop proxy priority;
• standard proxy environment precedence;
• macOS HTTPS and HTTP system proxy discovery;
• system proxy bypass behavior;
• non-macOS fallback behavior;
• proxy propagation to the Git command and subprocess environment;
• environment-only propagation for credentialed proxies;
• unchanged command shape when no proxy is selected;
• proxy-credential redaction in diagnostics;
• URL-encoded proxy-credential redaction;
• GitHub token redaction from errors.

Validation performed:

python3 -m unittest discover -s tests -v
Ran 13 tests ... OK

python3 -m compileall -q gitdrop tests
git diff --check

A local Git integration check also confirmed that the per-command http.proxy value is visible to Git.

Added tests/__init__.py so standard root-level unittest discovery finds the suite. A new pull-request test workflow runs the suite automatically, and release builds now run the same tests before packaging.

Documentation

Added a macOS proxy troubleshooting section covering Shadowrocket, Clash, Surge, Fake-IP/TUN behavior, proxy precedence, and the explicit GITDROP_HTTPS_PROXY override.

Security

TLS verification remains enabled. The implementation does not:

• disable http.sslVerify;
• place the GitHub token in command-line arguments;
• place credentialed proxy URLs in command-line arguments;
• modify global Git proxy configuration;
• store proxy credentials in repository remotes or diagnostics.

Closes #3.

[jiale-wangOwO]

????:????????(Request changes)?

1. [P2] ??????????????
   gitdrop/git_sync.py ? _run() ????? URL ?? git -c http.proxy=...???? URL ????????,??????????????????????????????? Git,????????????? URL,???????????????

2. [P2] ?? Git ????????????
   ????? GitHub Token?? Git ? stderr ?????? URL,_proxy_display_name() ??????????,???????????????????(?? URL ????)???????

3. [P3] ?????????????
   ?? 11 ???????????,??? unittest discover ????????,Release workflow ???????????? tests/__init__.py,?? CI/release workflow ??????

??????macOS ???????bypass ??? README ?????????????

The review text was corrupted by an encoding issue. Superseded by a corrected UTF-8 review.

[jiale-wangOwO]

审阅结论：建议先修改后合并。

1. [P2] 代理账号密码会出现在进程命令行中。_run() 把完整代理 URL 放进 git -c http.proxy=...。如果 URL 含用户名和密码，其他本地进程可能读取凭据。建议不要把含凭据的代理 URL 放入命令行。

2. [P2] Git 原始错误可能泄露代理密码。当前只脱敏 Token；如果 stderr 回显完整代理 URL，_proxy_display_name() 只保护追加提示，不能保护原始错误。建议展示错误前同时脱敏代理凭据及其 URL 编码形式。

3. [P3] 新增测试没有接入自动流程。11 个测试可单独运行并通过，但标准 unittest discover 当前发现不到测试，Release workflow 也没有执行测试。建议增加 tests/__init__.py 并在 CI 中运行测试。

代理优先级、macOS 系统代理读取、bypass 处理和 README 说明暂未发现其他阻塞问题。