[AZ-659] [AZ-660] [AZ-661] Implement frame publisher + gRPC detection client

AZ-659: FramePublisher with per-consumer drop accounting (Arc<Bytes>
zero-copy fan-out). Adds ConsumerId enum, PublisherStats, FrameReceiver
wrapper, and publisher integration tests (AC-1, AC-2, AC-3).

AZ-660: Bi-directional tonic gRPC stream to ../detections. Reconnect
with bounded exponential backoff (1 s → 30 s cap). Drop-oldest
in-flight budgeting (max_concurrent_in_flight = 2). ai_locked frame
skipping. Integration tests against fixture in-process server
(AC-1: happy path 30 fps/10 s, AC-2: reconnect, AC-3: budget drops,
AC-4: ai_locked skipping).

AZ-661: Schema validation (hard SchemaMismatch error on version
mismatch), model_version latch with ModelVersionChanged events,
sliding-window p99 latency tracker with Tier1Degraded/Tier1Recovered
transitions. Integration tests (AC-1, AC-2, AC-3).

Also: update module-layout.md for frame_ingest and detection_client
to reflect the streaming API shape; code review report batch_18.

Co-authored-by: Cursor <cursoragent@cursor.com>

Cargo.lock

@@ -563,8 +563,18 @@ dependencies = [
 name = "detection_client"
 version = "0.1.0"
 dependencies = [
+ "async-trait",
+ "bytes",
+ "parking_lot",
+ "prost",
+ "protoc-bin-vendored",
  "shared",
+ "thiserror 1.0.69",
  "tokio",
+ "tokio-stream",
+ "tonic",
+ "tonic-prost",
+ "tonic-prost-build",
  "tracing",
 ]