clink v0.1.0

Initial public release: the engine as described in the README.

Naming, settled for 1.0: the cluster roles are the coordinator (control
plane) and workers (subtask hosts), clink_node --role=coordinator|worker;
the fluent API entry point is clink::api::Pipeline; the in-process test
cluster is clink::test::TestCluster. Domain vocabulary (watermarks, windows,
checkpoints, savepoints, keyed state, key groups, slots) is unchanged.

In brief:

• Typed operator DAG and fluent API on a local runtime and a distributed
  Coordinator/Worker runtime (TLS/mTLS, HA, HTTP API + dashboard).
• Event time end to end: watermarks, tumbling/sliding/session windows,
  interval joins, CEP.
• Keyed and broadcast state over in-memory, file-backed, RocksDB, and
  changelog backends; rescale, schema evolution, savepoints.
• Exactly-once checkpointing with true 2PC sinks (file, Kafka, Parquet,
  S3, Postgres) and an effectively-once upsert family.
• Arrow-native columnar wire format and columnar operator fast paths.
• SQL frontend: embedded (clink run, libclink C ABI, pyclink, Flight
  SQL) or submitted to a cluster.
• Deterministic incident replay: flight recorder, state-diff,
  replay --verify, frozen regression bundles.
• State as data: snapshots are Arrow IPC; export to Parquet/Iceberg;
  queryable live state.
• Connector suite across messaging, object storage, table formats,
  databases, and HTTP endpoints (see docs/connectors/).
• Public testing framework (clink::test), Kubernetes Helm chart and
  operator, reproducible benchmark harnesses.