fix: 完善 Bun 安装并修复 fzf 预览路径

[ChangeHow]

问题

• Bun 原先未纳入前端工具安装、完成状态检测和托管 PATH，导致 setup 无法完整安装或验证 Bun。
• fzf Ctrl-T 预览脚本中的路径变量在配置被 source 时提前展开，导致预览运行时无法基于当前选择和工作目录解析目标。

修改

• 增加 Bun 的可选安装、完成状态检测、verify 检查及 ~/.bun/bin PATH 配置。
• 转义 fzf 预览脚本变量，将路径解析推迟到 fzf 实际运行时。
• 同步中英文 README，并补充相关回归测试。

验证

• npm test（22 个测试文件、234 个测试通过）
• git diff --check

[gemini-code-assist]

Code Review

This pull request adds support for installing Bun as a frontend tool, updating the setup wizard, verification checks, documentation, and adding Bun's bin directory to the shell PATH configuration. It also fixes an issue in configs/shared/tools/fzf.zsh by escaping variables to defer their evaluation until fzf runs. Feedback on the changes highlights a logic issue where requiring Bun to be installed to mark the frontend step as completed will break the setup's idempotency for users who choose not to install Bun. Additionally, it is suggested to update the Bun installation failure warning to mention checking for the unzip dependency on Linux.

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[github-actions]

Zsh startup benchmark

Ubuntu 24.04 with Linuxbrew, atuin, fnm, fzf, zoxide, zinit, and the shipped plugins. Lower is better.

Warm startup (daily use)

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
current (a4894e7)	92.5 ± 0.6	91.4	93.8	1.00
main (4a52135)	92.6 ± 0.8	91.1	94.4	1.00 ± 0.01
previous commit (1b23357)	92.8 ± 4.4	89.4	109.1	1.00 ± 0.05

Cache-miss startup

Completion and tool-init caches are removed before every run; installed tools and plugins remain.

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
current (a4894e7)	697.4 ± 10.4	689.8	726.2	1.00 ± 0.02
main (4a52135)	694.4 ± 2.2	690.8	698.0	1.00
previous commit (1b23357)	697.3 ± 4.6	690.9	707.3	1.00 ± 0.01