fix: release port 1455 when OAuth server fails to bind

[tryHivemind]

Summary

Fixes #102 — when http.Server emits an error event on .listen() (e.g. EADDRINUSE because another process holds port 1455), the error handler was resolving the promise with ready: false but never calling server.close(). This left the port in a half-open state, so the OS kept it claimed even though we gave up on it. Any subsequent auth attempt would also fail to bind, and the callback URL http://127.0.0.1:1455 would refuse connections.

Root cause in lib/auth/server.ts:

// before
.on("error", (err) => {
    // ...log...
    resolve({ ready: false, close: () => { try { server.close() } catch {} }, ... });
    // port never released here ↑
});

// after
.on("error", (err) => {
    // ...log...
    server.close();   // ← release immediately
    resolve({ ready: false, close: () => { try { server.close() } catch {} }, ... });
});

Test plan

• Manually occupy port 1455 (nc -l 1455), then run opencode auth login → should fall back to manual paste without hanging
• Run auth twice in quick succession → second attempt should not get EADDRINUSE from the first