fix(build): 更新 electron / electron-builder 二进制镜像地址

[Albert0516]

背景

旧 electron_mirror（npmmirror.com/mirrors/electron/）已不稳定，下载 Electron 二进制常超时，影响本地打包 / CI 打包。

改动（仅 .npmrc）

• electron_mirror → https://registry.npmmirror.com/-/binary/electron/（新可用地址）
• 新增 electron_builder_binaries_mirror → https://registry.npmmirror.com/-/binary/electron-builder-binaries/，避免 pnpm package 时下载 nsis / winCodeSign 等 electron-builder 二进制超时。

影响面

仅打包/安装期镜像配置，不动任何运行时代码；registry（npm 包源）不变。

验证

• 配置项为 electron / electron-builder 官方认可的镜像变量名。
• 建议合并前在本机或 CI 跑一次 pnpm package（或触发 release 流程的下载步骤）确认两个镜像可达、不再超时。

与预下载功能（#178）无关，独立提交以便快速合并、不互相阻塞。

🤖 Generated with Claude Code

[github-actions]

Affected Areas & Test Selection

No area matched. Only P0 specs will run as baseline.

Changed files: 1

• .npmrc

Top changed symbols (by caller count):

Symbol	Kind	Callers

E2E specs that will run on this PR:

• (P0 baseline only — see apps/web/e2e/area-map.json)

---

Generated by Impact Analysis workflow. This is informational, not a gate.

[github-actions]

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[ocr] Session: 936470b5-7dd7-4f19-8d55-b152a731ec9d (retry with: --resume 936470b5-7dd7-4f19-8d55-b152a731ec9d)
Error: review failed: all 1 file review(s) failed — check your LLM configuration and API key