ci: Replace bun with pnpm

[MikuroXina]

• Replace bun in scripts with pnpm
• Update docs

close #

Type of Change:

Cause of the Problem (問題の原因)

Dealing with Problems (問題への対処)

Details of implementation (実施内容)

Additional Information (追加情報)

[cloudflare-workers-and-pages]

Deploying oreorebot2 with    Cloudflare Pages

Latest commit:	bda62dd
Status:	🚫  Build failed.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.93%. Comparing base (5d4e656) to head (bda62dd).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1525   +/-   ##
=======================================
  Coverage   48.93%   48.93%           
=======================================
  Files         112      112           
  Lines        5023     5023           
  Branches      518      518           
=======================================
  Hits         2458     2458           
  Misses       2048     2048           
  Partials      517      517           

Flag	Coverage Δ
unittests	48.93% <ø> (ø)

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