fix(utils): replace randomIdString() with deterministic createElementId()

[caugner]

Description

Remove randomIdString() in favor of a deterministic createElementId() function.

Motivation

Increase chances of HTML files being identical on subsequent builds, speeding up the sync part of the deployment.

Additional details

Tested locally with the following script:

# 1. Build rari content (once)
BUILD_OUT_ROOT=./out node --env-file=.env --run rari -- build

# 2. Build Fred JS/CSS bundles (once)
BUILD_OUT_ROOT=./out npm run build

# 3. First SSR run → save HTML to build1/
BUILD_OUT_ROOT=./out npm run ssr
rsync -a --include="*/" --include="*.html" --exclude="*" ./out/ ./build1/
find ./out -name "*.html" -not -path "*/static/*" -delete

# 4. Second SSR run → save HTML to build2/
BUILD_OUT_ROOT=./out npm run ssr
rsync -a --include="*/" --include="*.html" --exclude="*" ./out/ ./build2/

# 5. Compare
diff -rq ./build1/ ./build2/

Only the homepage and the Playground had differences:

$ diff -rq ./build1/ ./build2/ 2>&1

Files ./build1/en-us/index.html and ./build2/en-us/index.html differ
Files ./build1/en-us/play/index.html and ./build2/en-us/play/index.html differ
Files ./build1/es/index.html and ./build2/es/index.html differ
Files ./build1/es/play/index.html and ./build2/es/play/index.html differ
Files ./build1/fr/index.html and ./build2/fr/index.html differ
Files ./build1/fr/play/index.html and ./build2/fr/play/index.html differ
Files ./build1/ja/index.html and ./build2/ja/index.html differ
Files ./build1/ja/play/index.html and ./build2/ja/play/index.html differ
Files ./build1/ko/index.html and ./build2/ko/index.html differ
Files ./build1/ko/play/index.html and ./build2/ko/play/index.html differ
Files ./build1/pt-br/index.html and ./build2/pt-br/index.html differ
Files ./build1/pt-br/play/index.html and ./build2/pt-br/play/index.html differ
Files ./build1/ru/index.html and ./build2/ru/index.html differ
Files ./build1/ru/play/index.html and ./build2/ru/play/index.html differ
Files ./build1/zh-cn/index.html and ./build2/zh-cn/index.html differ
Files ./build1/zh-cn/play/index.html and ./build2/zh-cn/play/index.html differ
Files ./build1/zh-tw/index.html and ./build2/zh-tw/index.html differ
Files ./build1/zh-tw/play/index.html and ./build2/zh-tw/play/index.html differ

Homepage differences:

$ diff ./build1/en-us/index.html ./build2/en-us/index.html

1933c1933
<               4 hours ago
---
>               5 hours ago
1953c1953
<               4 hours ago
---
>               5 hours ago
1973c1973
<               4 hours ago
---
>               5 hours ago
1993c1993
<               1 hour ago
---
>               2 hours ago
2013c2013
<               20 minutes ago
---
>               2 hours ago
`

Playground differences:

```console
$ diff ./build1/en-us/play/index.html ./build2/en-us/play/index.html

1420c1420
<          lit$391985138$0 run-on-start run-on-change defer-hydration><template shadowroot="open" shadowrootmode="open"><style>
---
>          lit$070035930$0 run-on-start run-on-change defer-hydration><template shadowroot="open" shadowrootmode="open"><style>
1562c1562
<       <!--lit-node 32--><mdn-modal   lit$391985138$20 class="share" defer-hydration><template shadowroot="open" shadowrootmode="open"><style>dialog{border:1px solid var(--color-border-primary);border-radius:.25rem;padding:0}header{display:flex;padding:.5rem}header h2{margin:0}header mdn-button{margin-left:auto}slot{display:block;padding:0 1rem 1rem}</style><!--lit-part 89wSBtjvN/w=-->
---
>       <!--lit-node 32--><mdn-modal   lit$070035930$20 class="share" defer-hydration><template shadowroot="open" shadowrootmode="open"><style>dialog{border:1px solid var(--color-border-primary);border-radius:.25rem;padding:0}header{display:flex;padding:.5rem}header h2{margin:0}header mdn-button{margin-left:auto}slot{display:block;padding:0 1rem 1rem}</style><!--lit-part 89wSBtjvN/w=-->
1647c1647
<       <!--lit-node 47--><mdn-modal   lit$391985138$29 class="report" defer-hydration><template shadowroot="open" shadowrootmode="open"><style>dialog{border:1px solid var(--color-border-primary);border-radius:.25rem;padding:0}header{display:flex;padding:.5rem}header h2{margin:0}header mdn-button{margin-left:auto}slot{display:block;padding:0 1rem 1rem}</style><!--lit-part 89wSBtjvN/w=-->
---
>       <!--lit-node 47--><mdn-modal   lit$070035930$29 class="report" defer-hydration><template shadowroot="open" shadowrootmode="open"><style>dialog{border:1px solid var(--color-border-primary);border-radius:.25rem;padding:0}header{display:flex;padding:.5rem}header h2{margin:0}header mdn-button{margin-left:auto}slot{display:block;padding:0 1rem 1rem}</style><!--lit-part 89wSBtjvN/w=-->

Related issues and pull requests

Fixes #913.

[github-actions]

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