[CLI] Avoid port conflicts when starting PHP-WASM network proxies

[chubes4]

What?

Binds php-wasm networking proxy servers directly on automatic ports (0) and reads back assigned ports, instead of probing free ports first and rebinding concrete ports later.

Why?

Fixes #3721.

The deeper root cause is in @php-wasm/node networking, not the top-level Playground CLI HTTP server:

• withNetworking() previously called findFreePorts(2).
• findFreePorts() opened temporary net.Server instances on 0, read their assigned ports, then closed them.
• The outbound websocket proxy later attempted to bind a new HTTP/WebSocket server to one of those concrete ports on 127.0.0.1.
• The inbound websocket proxy used the same preselected concrete port pattern through addTCPServerToWebSocketServerClass().
• Those probe-then-bind gaps are inherently racy. On a host with many local listeners, another process can already own or claim the selected concrete port by the time a proxy binds it.

Tracing a downstream WP Codebox smoke test showed the relevant outbound sequence:

[listen:http] args=0
    at app.listen (.../express/lib/application.js:635:24)
    at startServer (.../packages/playground/cli/src/start-server.ts:46:5)
[listen:http:listening] address={"address":"::","family":"IPv6","port":55974}

[listen:net] args=0
    at listenOnRandomPort (.../node_modules/@php-wasm/node/index.js:93:12)
    at findFreePorts (.../node_modules/@php-wasm/node/index.js:79:26)
    at withNetworking (.../node_modules/@php-wasm/node/index.js:365:71)

[listen:http] args=55976, "127.0.0.1"
    at initOutboundWebsocketProxyServer (.../node_modules/@php-wasm/node/index.js:162:15)
    at withNetworking (.../node_modules/@php-wasm/node/index.js:366:44)

So the CLI was already passing 0 correctly for its main server. The collision came from php-wasm choosing concrete “free” proxy ports before actually starting those proxies.

How?

• Starts the outbound websocket proxy with listenPort = 0.
• Reads the assigned outbound websocket proxy port from the started server and uses that port in generated websocket URLs.
• Starts the inbound websocket proxy with options.port = 0 inside the server decorator.
• Reads the assigned inbound websocket proxy port after the websocket server is listening and uses that port for the TCP bridge.
• Defers the inbound ready callback until both the websocket server and TCP bridge are listening, while preserving the callback this binding.
• Closes the inbound TCP bridge when the decorated websocket server closes.
• Removes the obsolete findFreePorts() helper and centralizes assigned-port lookup in getServerPort().
• Adds error rejection to outbound proxy startup so bind failures propagate.
• Adds regression coverage verifying both inbound and outbound websocket proxies bind directly to automatic ports.

Testing

• npx nx typecheck php-wasm-node
• npx vitest run packages/php-wasm/node/src/test/networking-port-allocation.spec.ts --config packages/php-wasm/node/vite.config.ts

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Traced the downstream failure, identified the php-wasm networking TOCTOU, drafted the focused fix and regression tests, did cleanup/review passes, and ran targeted verification; Chris remains responsible for review and merge.

[brandonpayton]

Thanks for this fix, @chubes4! It makes sense, reads well, and tests well. Let's merge.