feat(version): derive data cache version from content hash of the data tree

Replace the hand-maintained DATA_VERSION constant with a build-time SHA-256
hash of static/data/ embedded as a 'version' field in the preload manifest.
The runtime reads it via fetchWithFallback and clears the IDB cache when it
differs, so any data edit auto-invalidates cached data — no manual bump to
forget. The no-version (offline/stale) and IDB read-error guards are kept,
so the cache is never wiped on an unreadable signal.

Closes audit item L1.

static/data/shared/preload-manifest.json

@@ -5260,5 +5260,6 @@
     "bible": [
       "/data/bible/versions.json"
     ]
-  }
+  },
+  "version": "7631e35da99e"
 }