Phase 1: storage + catalog layer

- storaged: object_store backend (LocalFileSystem), PUT/GET/DELETE/LIST endpoints
- shared: arrow_helpers with Parquet roundtrip + schema fingerprinting (2 tests)
- catalogd: in-memory registry with write-ahead manifest persistence to object storage
- catalogd: POST/GET /datasets, GET /datasets/by-name/{name}
- gateway: wires storaged + catalogd with shared object_store state
- Phase tracker updated: Phase 0 + Phase 1 gates passed

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/shared/Cargo.toml

@@ -9,3 +9,7 @@ serde_json = { workspace = true }
 thiserror = { workspace = true }
 uuid = { workspace = true }
 chrono = { workspace = true }
+arrow = { workspace = true }
+parquet = { workspace = true }
+bytes = { workspace = true }
+sha2 = { workspace = true }