fix(engine): carry programmatic forceScreenshot opt-out to concrete-resolved site

Miguel R3 blocker on #2359: the runtime helper only checked the env opt-out
(PRODUCER_FORCE_SCREENSHOT=false), silently defeating the documented
programmatic escape hatch (overrides.forceScreenshot === false) on the
browserGpuMode:'auto' → software probe path. At the concrete-resolution
site the boolean forceScreenshot === false is ambiguous between default
and explicit opt-out — resolveConfig sees the provenance but the runtime
helper does not.

Fix: persist provenance on the resolved config.

- New INTERNAL EngineConfig field forceScreenshotExplicitlyOptedOut, set
  by resolveConfig when EITHER env or programmatic explicit-false is
  present. Purpose-documented in the type as 'not intended to be set by
  callers'.
- shouldClampToScreenshotForConcreteGpu gains an opts.programmaticOptOut
  parameter; returns false early when set. Env stays as the third arg
  (backward compatibility with existing tests).
- frameCapture.ts and renderOrchestrator.ts pass
  config.forceScreenshotExplicitlyOptedOut through at both call sites, so
  the auto→software probe path preserves the same escape hatches as
  literal browserGpuMode:'software'.

New tests: 5 additional cases across the helper (programmatic opt-out
alone; programmatic beats missing env) and resolveConfig provenance
(programmatic sets flag; env sets flag; neither leaves it undefined).
Local: 61/61 engine config tests pass (was 56).

packages/producer/src/services/renderOrchestrator.ts

@@ -1914,13 +1914,16 @@ export async function executeRenderJob(
     // that probe to software: `resolveConfig` couldn't see this at config
     // time, so `captureObservability.forceScreenshot` was still false,
     // misreporting `captureMode: "beginframe"` for a session that will
-    // actually take the screenshot path. Env-level opt-out preserved via
-    // the shared helper.
+    // actually take the screenshot path. Both env and programmatic opt-outs
+    // preserved via the shared helper (the programmatic one carried on the
+    // config as `forceScreenshotExplicitlyOptedOut`).
     const observabilityForceScreenshot =
       captureObservability.forceScreenshot ||
       shouldClampToScreenshotForConcreteGpu(
         resolvedBrowserGpuMode,
         captureObservability.forceScreenshot,
+        process.env,
+        { programmaticOptOut: cfg.forceScreenshotExplicitlyOptedOut ?? false },
       );
     updateCaptureObservability({
       browserGpuMode: resolvedBrowserGpuMode,