fix: Remove duplicate context variable declarations in benchmark tests

Fixed compilation errors in benchmark test files where `ctx` was
declared twice, preventing benchmarks from running.

Changes:
- internal/storage/sqlite/bench_helpers_test.go: Remove duplicate ctx declaration
- internal/storage/sqlite/compact_bench_test.go: Remove duplicate ctx declaration

This allows `go test -tags=bench` to compile and run successfully.

Related to bd-5qim verification.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/storage/sqlite/compact_bench_test.go

@@ -127,7 +127,6 @@ func setupBenchDB(tb testing.TB) (*SQLiteStorage, func()) {
 		tb.Fatalf("Failed to create storage: %v", err)
 	}
 
-	ctx := context.Background()
 	if err := store.SetConfig(ctx, "issue_prefix", "bd"); err != nil {
 		tb.Fatalf("Failed to set issue_prefix: %v", err)
 	}