Add IPFS/Helia integration for block providing and RASL endpoint
Blocks and blobs are now stored in a Helia-managed FsBlockstore and
announced on the DHT. A new /.well-known/rasl/:cid endpoint serves
content-addressed blocks over HTTP with immutable caching. IPFS
operations are fire-and-forget and never block the commit path.
Existing blocks are backfilled on startup. Controlled via
IPFS_ENABLED and IPFS_NETWORKING env vars.