fix(updater): 修复更新请求代理支持

[sunerpy]

变更

• 启用 reqwest 系统代理与 SOCKS 支持，允许配置 http://、https://、socks5:// 更新代理
• 保存前校验代理 URL，并在检查与下载阶段复用同一代理策略
• 将网络故障映射为可诊断的 network 错误，同时隐藏代理认证信息
• 增加前端三态、代理流量证明和 Windows 分发回归测试

验证

• make lint
• make test-unit
• make coverage-gate（总行覆盖率 93.20%，updater.rs 97.69%）
• cargo xwin check -p agentlens-tauri --tests --target x86_64-pc-windows-msvc
• make dist-windows
• make dist-windows-manifest-verify
• make updater-manifest-verify
• Playwright 代理 system/custom/invalid 三态截图人工验收
• 代理实测观察到 manifest 与 artifact 两个请求均经过自定义 HTTP 代理

[codecov]

Codecov Report

❌ Patch coverage is 98.24561% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src-tauri/src/updater.rs	98.23%	5 Missing ⚠️

Files with missing lines	Coverage Δ
src-tauri/src/commands.rs	96.49% <100.00%> (+<0.01%)	⬆️
src-tauri/src/contract.rs	95.41% <ø> (ø)
src-tauri/src/updater.rs	98.82% <98.23%> (-0.57%)	⬇️

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