v0.15.0

Features
- Content-addressed filesystem snapshots with labels and reflog (#169)
- Per-session filesystem that auto-restores like the heap, and cross-worker
  snapshot loading so sessions can be forked from another worker's heap+fs
  (#171, #172)
- Non-voting learner cluster nodes for ephemeral per-session workers (#170)
- S3-compatible object stores: AWS_ENDPOINT_URL + AWS_S3_FORCE_PATH_STYLE
  (MinIO, LocalStack, etc.)
- TypeScript client generated from the OpenAPI spec (#168)

Fixes
- fs ops run on the current-thread isolate runtime (no more aborts on pending
  ops); S3 client dispatched on its owning runtime; fs blobs pre-staged into the
  local cache before execution so in-op reads never await remote I/O.