[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>

crates/detection_client/Cargo.toml

@@ -6,11 +6,24 @@ rust-version.workspace = true
 license.workspace = true
 publish.workspace = true
 authors.workspace = true
+build = "build.rs"
 
 [dependencies]
 shared = { workspace = true }
 tokio = { workspace = true }
+tokio-stream = { workspace = true }
 tracing = { workspace = true }
+async-trait = { workspace = true }
+thiserror = { workspace = true }
+bytes = { workspace = true }
+parking_lot = { workspace = true }
+prost = { workspace = true }
+tonic = { workspace = true }
+tonic-prost = { workspace = true }
 
-# Real gRPC stack lands with AZ-660 (`detection_client_grpc_stream`).
-# tonic / prost dependencies + build.rs + proto/ wiring will be added there.
+[build-dependencies]
+tonic-prost-build = { workspace = true }
+protoc-bin-vendored = { workspace = true }
+
+[dev-dependencies]
+tokio = { workspace = true, features = ["test-util"] }