fix: Windows support — Node.js server fallback for Playwright

[sozairali]

Summary

• /browse is completely non-functional on Windows due to two Bun bugs:
  • oven-sh/bun#4253 — child_process.spawn with stdio: ["pipe"] broken on Windows (Playwright can't launch Chromium)
  • oven-sh/bun#9911 — WebSocket client broken on Windows (Playwright can't connect() to a separately-launched Chromium either)
• On Windows, the CLI now spawns node server-node.mjs instead of bun run server.ts. The Node server is transpiled from the same source with a Bun API polyfill (Bun.serve → http.createServer, Bun.spawnSync → child_process.spawnSync, etc.)
• macOS/Linux behavior is completely unchanged
• Also fixes resolveServerScript() which excluded Windows paths (startsWith('/') fails for drive letters like C:\)

What's included

File	Change	Rationale
browse/src/cli.ts	Detect Windows, resolve Node server bundle, spawn node instead of bun	The CLI is the entry point that decides how to launch the server. Since Bun can't run Playwright on Windows at all (neither pipes nor WebSocket work), the server must run under Node. The CLI is the right place for this routing decision — it already handles server lifecycle. Also fixes a pre-existing bug where resolveServerScript() used startsWith('/') to detect dev mode, which excluded Windows paths like C:\....
browse/src/bun-polyfill.cjs	Polyfills Bun.serve, Bun.spawn, Bun.spawnSync, Bun.sleep for Node	The transpiled server code still calls Bun APIs (Bun.serve(), etc.) since it's generated from the same source. Rather than maintaining a separate Node fork of the server, this shim lets the same code run on both runtimes. Written as .cjs so it can be require()'d before the ESM server bundle executes. Only covers the 4 APIs the server actually uses — not a general-purpose Bun polyfill.
browse/scripts/build-node-server.sh	Build script: transpile + post-process + inject polyfill header	Automates producing server-node.mjs from the same source as the Bun server. Uses bun build --target=node for transpilation, then sed to handle two things that can't be polyfilled at runtime: import.meta.dir (Bun-only, replaced with a __dirname equivalent) and bun:sqlite (macOS-only cookie import, stubbed out since it's irrelevant on Windows). Runs as part of bun run build so the Node bundle stays in sync with the Bun binary.
package.json	Add Node server build to bun run build	Ensures the Node server bundle is always rebuilt alongside the Bun binary. Without this, the Node bundle could go stale after source changes.
setup	Windows: verify Chromium via Node (not Bun), require Node.js, clear error messages	The existing ensure_playwright_browser function tries to launch Chromium via Bun to verify it works — on Windows this hangs forever. Changed to use Node for the verification on Windows. Also added a Node.js requirement check with an actionable error message, since Node is now a runtime dependency on Windows.

This is a workaround

When Bun fixes their Windows pipe/WebSocket handling, the entire Node fallback can be deleted — one IS_WINDOWS check removed and everything goes back to running on Bun everywhere.

Test plan

Tested on Windows 11 (Git Bash, Bun 1.3.11, Node 22.16.0):

• bun run dev goto https://example.com — navigates successfully
• bun run dev text — returns page content
• bun run dev snapshot -i — returns interactive elements with @refs
• bun run dev fill @e1 "query" + click @e2 — form interaction works
• bun run dev console --errors — error monitoring works
• bun run dev network — network log works
• Multi-command session against persistent server — state preserved between commands
• Tested against live site (lantbot.ozairali.com) — full chat interaction worked end-to-end
• Verify macOS/Linux is unaffected (no IS_WINDOWS code path taken)

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