[AZ-675] telemetry_stream Tonic gRPC server + per-client lossy queue

Pins operator-link transport to gRPC server-streaming (closes
architecture Q2 in favour of gRPC). Adds first-time tonic / prost /
tonic-build infrastructure to the workspace; uses
protoc-bin-vendored so neither dev machines nor CI need system
protoc installed.

Design — back-pressure lives in the per-topic tokio::sync::broadcast
ring, drained directly by the tonic-streamed response via
BroadcastStream + StreamMap. No intermediate mpsc buffer that could
absorb back-pressure invisibly. Slow client overrun -> Lagged(n)
event -> per-(client_id, topic) drop counter incremented; healthy
clients on the same topic are unaffected.

Service surface — Subscribe(SubscribeRequest) -> stream
TelemetryMessage; five topics (TelemetrySample, GimbalState,
DetectionEvent, MovementCandidate, MapObjectsBundle); empty topics
list defaults to subscribe-all; empty client_id rejected; stream
drop decrements subscribed_clients via StreamGuard. TelemetrySink
push_detections is now real; push_frame still NotImplemented(AZ-676
video path).

Tests — 6 unit + 5 integration (AC-1..AC-3 via in-process gRPC
client, plus subscribe-all default + empty-client_id rejection).
Clippy on telemetry_stream clean.

Pre-existing mission_executor ac3 test polling race surfaces more
reliably under the new tonic build pressure; documented as
_docs/_process_leftovers/2026-05-20_mission_executor_ac3_flake.md
and unchanged by this batch.

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

crates/telemetry_stream/Cargo.toml

@@ -6,9 +6,27 @@ 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 }
+serde = { workspace = true }
+serde_json = { workspace = true }
+prost = { workspace = true }
+tonic = { workspace = true }
+tonic-prost = { workspace = true }
+parking_lot = { workspace = true }
+uuid = { workspace = true }
+chrono = { workspace = true }
+
+[build-dependencies]
+tonic-prost-build = { workspace = true }
+protoc-bin-vendored = { workspace = true }
+
+[dev-dependencies]
+tokio = { workspace = true, features = ["test-util"] }