feat(observability): add #[instrument] tracing to all gRPC service handlers

Add tracing::instrument(skip_all) to gRPC handlers across all services
for distributed trace spans via OTLP. Pairs with Prometheus scrape
annotations from previous commit.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

services/backtesting_service/src/service.rs

@@ -6,7 +6,7 @@ use std::sync::Arc;
 use tokio::sync::{broadcast, RwLock};
 use tokio_util::sync::CancellationToken;
 use tonic::{Request, Response, Status};
-use tracing::{debug, error, info};
+use tracing::{debug, error, info, instrument};
 use uuid::Uuid;
 
 use crate::foxhunt::tli::{backtesting_service_server::BacktestingService, *};
@@ -362,6 +362,7 @@ impl BacktestingService for BacktestingServiceImpl {
     >;
 
     /// Start a new backtest
+    #[instrument(skip_all)]
     async fn start_backtest(
         &self,
         request: Request<StartBacktestRequest>,
@@ -444,6 +445,7 @@ impl BacktestingService for BacktestingServiceImpl {
     }
 
     /// Get backtest status
+    #[instrument(skip_all)]
     async fn get_backtest_status(
         &self,
         request: Request<GetBacktestStatusRequest>,
@@ -469,6 +471,7 @@ impl BacktestingService for BacktestingServiceImpl {
     }
 
     /// Get backtest results
+    #[instrument(skip_all)]
     async fn get_backtest_results(
         &self,
         request: Request<GetBacktestResultsRequest>,
@@ -547,6 +550,7 @@ impl BacktestingService for BacktestingServiceImpl {
     }
 
     /// List historical backtests
+    #[instrument(skip_all)]
     async fn list_backtests(
         &self,
         request: Request<ListBacktestsRequest>,
@@ -573,6 +577,7 @@ impl BacktestingService for BacktestingServiceImpl {
     }
 
     /// Subscribe to backtest progress
+    #[instrument(skip_all)]
     async fn subscribe_backtest_progress(
         &self,
         request: Request<SubscribeBacktestProgressRequest>,
@@ -610,6 +615,7 @@ impl BacktestingService for BacktestingServiceImpl {
     }
 
     /// Stop a running backtest
+    #[instrument(skip_all)]
     async fn stop_backtest(
         &self,
         request: Request<StopBacktestRequest>,