Use content-hashed filenames for production static assets

Production previously served static assets with long-lived immutable caching while reusing the same filenames across deployments. This could cause browsers to combine a new HTML document with outdated JavaScript, CSS, or worker files.

Commit 69b3786b mitigated the problem by requiring static assets to be revalidated. This is a short-term workaround rather than the intended long-term caching strategy.

A future build/deployment improvement should:

- generate content-hashed filenames for JavaScript, CSS, and worker assets;
- update generated HTML and worker references accordingly;
- restore long-lived immutable caching for hashed assets.

This is not currently blocking production, but would provide reliable cache invalidation without sacrificing long-term caching.