fix(warp): attach CONNECT proxy to main server and reuse running instance

[garrettg123]

Summary

This PR enables the CONNECT forward proxy and absolute-form HTTP handlers directly on pxpipe-proxy's main server (default port 47821) and updates pxpipe warp to reuse an already-running pxpipe instance on 127.0.0.1:<port> when available.

Problem

1. When running tools with persistent background daemons (such as Claude Code's background supervisor daemon and agents), running pxpipe warp spawns a temporary CONNECT proxy on an ephemeral port (port 0).
2. The background daemon inherits HTTP_PROXY=http://127.0.0.1:<ephemeral_port>.
3. When the foreground warp process exits, the ephemeral port stops listening. The long-running daemon and its spawned background workers remain pointing at the dead port, leading to ECONNREFUSED / "Connection refused — a firewall or proxy may be blocking it" on subsequent prompts.
4. Multiple concurrent agent sessions each allocated separate ephemeral ports, causing port contention and broken daemon routing.

Fix

• Attach handlers.handleConnect (server.on('connect', ...)) and handlers.handleAbsoluteForm to the main createServer in src/node.ts.
• In createWarpRuntime (src/warp/index.ts), probe 127.0.0.1:${port} before starting an ephemeral listener; if the proxy is already running on that port, reuse it directly.
• Added automated integration test (tests/warp-connect.test.ts) validating HTTPS CONNECT proxy tunneling and local route diversion.

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