Auto-bust sx.js and body.js via MD5 hash instead of manual version string

Computes file content hash at process startup, cached for lifetime.
Removes manual cache-busting instruction from CLAUDE.md.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -5,7 +5,6 @@ Cooperative web platform: federated content, commerce, events, and media process
 ## Deployment
 
 - **Do NOT push** until explicitly told to. Pushes reload code to dev automatically.
-- **Cache busting:** After editing `sx.js`, bump the `?v=` query string in `shared/sx/helpers.py` (search for `sx.js?v=`).
 
 ## Project Structure