iwsdk-vite-plugin-dev: use waitUntil:'commit' for managed-browser navigation

Summary:
`launchManagedBrowser` in `packages/vite-plugin-dev/src/headless-browser.ts` previously did `page.goto(url, { waitUntil: 'networkidle' })` followed immediately by `page.waitForFunction(() => window.IWER_DEVICE !== undefined, { timeout: 15000 })`.

`networkidle` is a heuristic — it resolves once Playwright observes >=500ms with no network activity. The IWSDK dev runtime opens a persistent WebSocket to `/__iwer_mcp` on load, and on Chromium builds where WebSocket frames count toward network activity (notably Playwright's fallback ubuntu-24.04-x64 chromium build), `networkidle` never fires. `page.goto` then times out at 30s with `browser_launch_failed`, even though the page reached `interactive` and IWER injected within ~800ms.

Switch to `waitUntil: 'commit'`. The subsequent `waitForFunction(IWER_DEVICE)` is the real readiness gate — it polls until the IWSDK dev runtime has finished injecting. No code between the two relies on intermediate `goto` state, so the caller's guarantee when `launchManagedBrowser` returns is unchanged.

`commit` + explicit `waitForFunction` is a more deterministic readiness contract than `networkidle` + same explicit wait: total wall-clock is identical on environments where `networkidle` was already firing (the explicit wait was the long pole), and it removes a class of "browser launches fine but `page.goto` times out" failures that are non-obvious to debug.

Reviewed By: zjm-meta

Differential Revision: D105639703

fbshipit-source-id: bcac4cb66896ca2fb09dd899e77044ece4f8e0d1

Author: felixtrz

packages/vite-plugin-dev/src/headless-browser.ts

@@ -373,7 +373,7 @@ export async function launchManagedBrowser(
     (window as any).__IWSDK_MCP_TRACE = traceEnabled;
   }, traceMcp);
 
-  await page.goto(url, { waitUntil: 'networkidle' });
+  await page.goto(url, { waitUntil: 'commit' });
 
   // Wait for IWER to inject and XR device to be available
   await page.waitForFunction(() => (window as any).IWER_DEVICE !== undefined, {