Add Galaxy repository API and clients

clients/python/README.md

@@ -98,6 +98,76 @@ MXAccess commands and preserve raw replies on typed command exceptions.
 Canceling a Python task cancels the client-side gRPC call or stream wait. It
 does not abort an in-flight MXAccess COM call inside the worker process.
 
+## Galaxy Repository Browse
+
+The `GalaxyRepositoryClient` wraps the read-only `GalaxyRepository` gRPC
+service. It lets callers test connectivity to the AVEVA System Platform
+Galaxy Repository (ZB SQL database), read the last deploy timestamp, and
+enumerate the deployed object hierarchy plus each object's dynamic
+attributes:
+
+```python
+from mxgateway import GalaxyRepositoryClient
+
+async with await GalaxyRepositoryClient.connect(
+    endpoint="localhost:5000",
+    api_key="<gateway-api-key>",
+    plaintext=True,
+) as galaxy:
+    if not await galaxy.test_connection():
+        raise RuntimeError("gateway cannot reach the Galaxy Repository DB")
+
+    last_deploy = await galaxy.get_last_deploy_time()
+    print(f"last deploy: {last_deploy}")
+
+    for obj in await galaxy.discover_hierarchy():
+        print(obj.tag_name, obj.contained_name)
+        for attr in obj.attributes:
+            print("  ", attr.attribute_name, "->", attr.full_tag_reference)
+```
+
+The methods return native Python types (`bool`, `datetime | None`, and a
+`list[GalaxyObject]` of generated proto messages) so callers can index
+into the hierarchy without learning the underlying stub class. The
+service requires the `metadata:read` scope on the API key.
+
+### Watching deploy events
+
+`GalaxyRepositoryClient.watch_deploy_events` opens a server-streaming
+subscription that emits the current cached deploy state immediately and
+then one `DeployEvent` per new Galaxy deploy. `sequence` is monotonic per
+gateway start; gaps mean events were dropped from the per-subscriber
+buffer. Pass `last_seen_deploy_time` to suppress the bootstrap event when
+the caller already has the current state cached:
+
+```python
+from datetime import datetime, timezone
+from mxgateway import DeployEvent, GalaxyRepositoryClient
+
+async with await GalaxyRepositoryClient.connect(
+    endpoint="localhost:5000",
+    api_key="<gateway-api-key>",
+    plaintext=True,
+) as galaxy:
+    last_seen: datetime | None = None
+    async for event in galaxy.watch_deploy_events(last_seen_deploy_time=last_seen):
+        assert isinstance(event, DeployEvent)
+        print(
+            f"#{event.sequence} deploy={event.time_of_last_deploy.ToDatetime(tzinfo=timezone.utc)} "
+            f"objects={event.object_count} attributes={event.attribute_count}"
+        )
+        if event.time_of_last_deploy_present:
+            last_seen = event.time_of_last_deploy.ToDatetime(tzinfo=timezone.utc)
+```
+
+The method returns an async iterator yielding the generated `DeployEvent`
+proto. Breaking out of the loop, calling `aclose()` on the iterator, or
+cancelling the surrounding task closes the underlying gRPC stream
+cleanly. The streaming RPC requires the same `metadata:read` scope as
+the other Galaxy methods. The CLI does not currently expose a
+streaming `watch-deploy-events` subcommand — use the library API
+directly when subscribing to deploy events from Python.
+
 ## Authentication And TLS
 
 `ClientOptions.api_key` adds this metadata to unary calls and streams: