fix: Cloudflare Pages function size

[jbmoelker]

Changes

• Adds postbuild logging for function size and total size for easier debugging (see below)
• Removes 404 function postbuild as it causes the workers.api.error.script_too_large (even though it's smaller than the permitted 1MiB); still we can live with a preview mode without a 404.

[post:function-sizes    ] 308K  functions/[locale]/[[path]].js
[post:function-sizes    ]  96K  functions/[locale]/[slug].js
...
[post:function-sizes    ] 136K  functions/robots.txt.js
[post:function-sizes    ] 2.9M  functions/

Associated issue

Resolves #123

How to test

1. Open a preview page like https://fix-function-size.head-start.pages.dev/en/overview-page/
2. Verify preview mode works

Checklist

• [x] I have performed a self-review of my own code
• [x] I have made sure that my PR is easy to review (not too big, includes comments)
• [x] I have made updated relevant documentation files (in project README, docs/, etc)
• I have added a decision log entry if the change affects the architecture or changes a significant technology
• [x] I have notified a reviewer

[cloudflare-pages[bot]]

Deploying with    Cloudflare Pages

Latest commit:	fb7a775
Status:	✅  Deploy successful!
Preview URL:	https://ffca73b8.head-start.pages.dev
Branch Preview URL:	https://fix-function-size.head-start.pages.dev

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