- Pod calls apply_materialization via gRPC after each successful FV,
  setting state to AVAILABLE_ONLINE. Server reads FV state post-completion
  to determine per-FV success/failure in batched SparkApplication runs.
- registry_address is now mandatory (simplified from complex path heuristic).
- Dockerfile rewritten to install feast from source (matches K8s engine pattern).
- Unit tests updated: 15/15 pass (3 new tests for _build_per_fv_jobs).
- E2E validated: 5 FVs x 9600 rows, 5 executors, all AVAILABLE_ONLINE.

Signed-off-by: Aniket Paluskar <apaluska@redhat.com>