feat: add initial

Signed-off-by: kjuulh <contact@kjuulh.io>

todos/SQ-011-subscribe-endpoint.md

@@ -0,0 +1,29 @@
+# SQ-011: Subscribe Endpoint (Single Node)
+
+**Status:** `[ ] TODO`
+**Blocked by:** SQ-010
+**Priority:** High
+
+## Description
+
+Implement the Subscribe gRPC RPC with server-streaming. Server pushes messages to the client as they become available.
+
+## Files to Create/Modify
+
+- `crates/sq-server/src/grpc/data_plane.rs` - DataPlaneService Subscribe impl
+
+## Behavior
+
+1. Client sends SubscribeRequest with topic, partition, optional start_offset
+2. Server reads from StorageEngine starting at the given offset
+3. Server streams batches of ConsumedMessage to the client
+4. When caught up, server polls for new messages at a configurable interval (e.g. 100ms)
+5. Stream continues until client disconnects or cancellation
+
+## Acceptance Criteria
+
+- [ ] Publish 10 messages, then subscribe from offset 0, receive all 10
+- [ ] Subscribe from offset 5, receive messages 5-9 only
+- [ ] Subscribe to empty topic from offset 0, then publish, receive new messages
+- [ ] Client disconnect: server-side stream cleans up without error
+- [ ] Subscribe to nonexistent topic: returns NotFound gRPC status