feat: ヘルプ埋め込みからドキュメントサイトのリファレンスに飛べるように

[m1sk9]

Type of Change:

新機能追加(ヘルプ)

Details of implementation (実施内容)

!help コマンドで表示される埋め込みのタイトルから各コマンドリファレンスに飛べるようにします。

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• Nextra 移行後の新ドキュメントサイトに対応
• すべてのコマンドヘルプでリファレンスに飛べるかどうか確認

[codecov-commenter]

Codecov Report

Merging #755 (faba0bf) into main (b74c595) will increase coverage by 0.22%.
The diff coverage is 98.27%.

@@            Coverage Diff             @@
##             main     #755      +/-   ##
==========================================
+ Coverage   72.13%   72.35%   +0.22%     
==========================================
  Files          71       71              
  Lines        4758     4800      +42     
  Branches      466      466              
==========================================
+ Hits         3432     3473      +41     
- Misses        861      862       +1     
  Partials      465      465              

Flag	Coverage Δ
unittests	72.35% <98.27%> (+0.22%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/service/command/meme.ts	74.83% <66.66%> (-0.34%)	⬇️
src/service/command/channel-info.ts	91.01% <100.00%> (+0.10%)	⬆️
src/service/command/command-message.ts	91.66% <100.00%> (+0.43%)	⬆️
src/service/command/debug.ts	86.36% <100.00%> (+0.20%)	⬆️
src/service/command/dice.ts	82.05% <100.00%> (+0.15%)	⬆️
src/service/command/guild-info.ts	94.60% <100.00%> (+0.02%)	⬆️
src/service/command/gyokuon.ts	77.77% <100.00%> (+0.56%)	⬆️
src/service/command/judging.ts	78.70% <100.00%> (+0.13%)	⬆️
src/service/command/kaere.ts	70.42% <100.00%> (+0.16%)	⬆️
src/service/command/kokusei-chousa.ts	93.10% <100.00%> (+0.12%)	⬆️
... and 23 more

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