CLI: session expires after ~1 hour due to OAuth client_id mismatch on token refresh #63

Problem

When using the CLI, sessions expire after approximately 1 hour. Running any command after that shows "Not logged in" even though the user previously authenticated successfully.

Root cause

The OAuth client_id for loopback clients includes the redirect URI with the port number. During sb login, a random free port is used (e.g., 54321), producing a client_id like:

http://localhost?redirect_uri=http%3A%2F%2F127.0.0.1%3A54321%2Fcallback&scope=...

When restoring sessions in getAgent(), a hardcoded port 0 is used instead:

http://localhost?redirect_uri=http%3A%2F%2F127.0.0.1%3A0%2Fcallback&scope=...

This produces a different client_id. When the access token expires (~1 hour TTL from the PDS) and the OAuth library tries to use the refresh token, the PDS rejects the request because the client_id doesn't match the one used during authorization.

Steps to reproduce

1. sb login <handle> — authenticate via browser
2. Use any command (e.g., sb cards) — works fine
3. Wait ~1 hour for the access token to expire
4. Run any command again — fails with "Not logged in"

Fix

Store the port used during login in session.json and reuse it when creating the NodeOAuthClient for session restoration. This keeps the client_id consistent so token refresh works correctly.

PR: #64