Adds JSON-RPC controller benchmark to complement Task 23's engine-level
benchmarks: end-to-end /fusion/assets/get_detail timing through the HTTP
dispatch layer.
Captured locally on westin-v19:
controller.get_detail: median=2ms p95=40ms (target <500ms, 12x headroom)
Tagged 'benchmark' so it stays out of fast unit runs.
Made-with: Cursor
