fix(engine): scale Chrome memory budget and frame cache to available RAM

On low-memory systems (<4GB free), Chrome's --force-gpu-mem-available-mb=4096
causes the renderer to allocate more GPU texture memory than the system can
provide, leading to OOM crashes during frame capture ("Target closed").

Changes:
- Scale --force-gpu-mem-available-mb to match available system RAM
  (512MB when <2GB free, 1024MB when <4GB, 4096MB otherwise)
- Add --js-flags=--max-old-space-size=N on low-memory systems to cap
  Chrome's V8 heap (256MB when <2GB free, 512MB when <4GB)
- Scale frame data URI cache defaults: 32 entries/128MB when <2GB free,
  64 entries/256MB when <4GB, unchanged otherwise

Closes #1072

packages/engine/src/services/browserManager.ts

@@ -8,7 +8,7 @@
 import type { Browser, PuppeteerNode } from "puppeteer-core";
 import { existsSync, readdirSync } from "fs";
 import { join } from "path";
-import { homedir } from "os";
+import { freemem, homedir } from "os";
 import { DEFAULT_CONFIG, type EngineConfig } from "../config.js";
 
 let _puppeteer: PuppeteerNode | undefined;
@@ -476,6 +476,24 @@ export function _setPuppeteerForTests(mock: PuppeteerNode | undefined): void {
   _puppeteer = mock;
 }
 
+function getFreeMb(): number {
+  return Math.floor(freemem() / (1024 * 1024));
+}
+
+function getGpuMemBudgetMb(): number {
+  const free = getFreeMb();
+  if (free < 2048) return 512;
+  if (free < 4096) return 1024;
+  return 4096;
+}
+
+function getLowMemoryFlags(): string[] {
+  const free = getFreeMb();
+  if (free >= 4096) return [];
+  const heapMb = free < 2048 ? 256 : 512;
+  return [`--js-flags=--max-old-space-size=${heapMb}`];
+}
+
 export interface BuildChromeArgsOptions {
   width: number;
   height: number;
@@ -530,9 +548,10 @@ export function buildChromeArgs(
     "--disable-print-preview",
     "--no-pings",
     "--no-zygote",
-    // Memory
-    "--force-gpu-mem-available-mb=4096",
+    // Memory — scale GPU budget to available system RAM
+    `--force-gpu-mem-available-mb=${getGpuMemBudgetMb()}`,
     "--disk-cache-size=268435456",
+    ...getLowMemoryFlags(),
     // Disable features that add overhead
     "--disable-features=AudioServiceOutOfProcess,IsolateOrigins,site-per-process,Translate,BackForwardCache,IntensiveWakeUpThrottling",
   ];