refactor(backend): Use request.routeOptions.url instead of request.routerPath to supress FSTDEP017

[AsPulse]

What

• close request.routerPathが非推奨になった影響で、警告 [FSTDEP017] が表示される (refactor) #11934
• fastifyのrequest.routerPathが使われているところをrequest.routeOptions.urlに書きかえています
  (一箇所だけでしたが……)

Why

• issueにもある通り、request.routerPathはFastifyの次のメジャーアップデートで削除される予定の非推奨プロパティです。
• 早急に変える必要は認められないといえばそうなのですが、
  このせいで警告FSTDEP017がリクエストごとにログに出てきて少し邪魔です……

Checklist

• Read the contribution guide
• Test working in a local environment

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (09dfb9b) 78.95% compared to head (008da6c) 78.92%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #11935      +/-   ##
===========================================
- Coverage    78.95%   78.92%   -0.03%     
===========================================
  Files          929      928       -1     
  Lines        99194    99089     -105     
  Branches      7889     7886       -3     
===========================================
- Hits         78318    78208     -110     
- Misses       20876    20881       +5     

Files	Coverage Δ
...ages/backend/src/server/web/ClientServerService.ts	88.25% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[syuilo]

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