fix(frontend): Enable to iterate over DOM collections

[woxtu]

What

dom.iterableを追加してHTMLCollectionをiterableにします。

Why

次のTypeScriptエラーを解決したい：

src/scripts/theme.ts(87,20): error TS2488: Type 'HTMLCollection' must have a '[Symbol.iterator]()' method that returns an iterator.

Additional info (optional)

Checklist

• [x] Read the contribution guide
• [ ] Test working in a local environment
• [ ] (If needed) Add story of storybook
• [ ] (If needed) Update CHANGELOG.md
• [ ] (If possible) Add tests

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 77.84%. Comparing base (f37d684) to head (fe1d580).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #14040 +/- ## =========================================== + Coverage 77.79% 77.84% +0.05% =========================================== Files 184 185 +1 Lines 25536 25600 +64 Branches 487 487 =========================================== + Hits 19865 19929 +64 Misses 5664 5664 Partials 7 7 ```

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[KisaragiEffective]

@syuilo マージしても良いですか and/or マージしますか？

[syuilo]

🙏