fix(producer): normalize error messages to prevent [object Object] in telemetry (#1099)

* fix(producer): normalize error messages to prevent [object Object] in telemetry

When a render fails and the caught value is a plain object (not an Error
instance), String(error) produces [object Object], masking the real error
in PostHog telemetry (~24 errors/day).

Add normalizeErrorMessage() that tries Error.message, string passthrough,
.message on plain objects, JSON.stringify, and String() as a last resort.
Apply it on the two telemetry-feeding paths: the main render failure
handler (renderOrchestrator.ts:2099) and buildRenderErrorDetails
(cleanup.ts), plus the error classifier isRecoverableParallelCaptureError
so timeout detection works even when the thrown value is a plain object.

* fix: address review — normalize CLI telemetry path, captureCost fallback

* fix: use local normalizeErrorMessage in CLI to avoid cross-package resolution

The Vite test runner can't resolve runtime imports from @hyperframes/producer
since its exports point to dist/. Copy the utility into the CLI package and
import locally instead.

packages/producer/src/utils/errorMessage.ts

@@ -0,0 +1,31 @@
+/**
+ * Normalize an unknown thrown value into a human-readable string.
+ *
+ * The default `String(error)` pattern produces `[object Object]` when the
+ * thrown value is a plain object — masking the real error in telemetry.
+ * This utility tries, in order:
+ *   1. `Error.message`
+ *   2. Raw string pass-through
+ *   3. `.message` property on a plain object
+ *   4. `JSON.stringify` for any other object
+ *   5. `String()` fallback for primitives (number, boolean, symbol, bigint)
+ *   6. `"unknown error"` for null / undefined
+ */
+export function normalizeErrorMessage(error: unknown): string {
+  if (error instanceof Error) return error.message;
+  if (typeof error === "string") return error;
+  if (typeof error === "object" && error !== null) {
+    const msg = (error as Record<string, unknown>).message;
+    if (typeof msg === "string") return msg;
+    try {
+      return JSON.stringify(error);
+    } catch {
+      try {
+        return `{${Object.keys(error as object).join(", ")}}`;
+      } catch {
+        /* truly opaque object */
+      }
+    }
+  }
+  return String(error ?? "unknown error");
+}