fix(engine): bucket gpu_renderer + cover the failure cohort (review)

Three review findings on the win32 drawElement PR:

1. gpu_renderer shipped the raw UNMASKED_RENDERER_WEBGL string — unbounded,
   driver-authored, GPU-model-specific, and |-joined across parallel
   sessions, i.e. high cardinality by construction, against this file's own
   convention of sanitizing engine-sourced strings (deGateReason is a
   bucket; error messages go through redactTelemetryString). Now bucketed at
   the source by classifyGpuRenderer to <backend>/<vendor>
   (metal/apple, d3d11/nvidia, swiftshader/other, ...), which is the whole
   analytic signal the win32 rollout needs and nothing else. The raw string
   never leaves the engine.

2. gpu_renderer reached render_complete only, so a crashed render — the
   cohort the field exists to attribute — carried no backend. It now rides
   RenderCaptureObservability (deGpuRenderer, sourced from the live probe
   session like the de_* counters), so both render_complete and
   render_error carry it and a hard failure still reports its GPU backend.
   On render_complete the perfSummary value still wins by spread order.

3. Restore the fallow-ignore-next-line suppression above
   __resetDeParallelRouterTrialStateForTests: CLI test files are not fallow
   entry points, so removing it fails the CI dead-code audit (local
   pre-commit passed only because of its changed-file scope).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

packages/cli/src/commands/render.ts

@@ -1102,6 +1102,7 @@ let deParallelRouterTrialFiredThisProcess = false;
  * resetting outside a test process where many independent test cases share
  * one imported module instance.
  */
+// fallow-ignore-next-line unused-export
 export function __resetDeParallelRouterTrialStateForTests(): void {
   deParallelRouterTrialManagedByUs = false;
   deParallelRouterTrialFiredThisProcess = false;