feat(cli): add saved remote servers

[opencode-agent]

Summary

• add named remote server profiles with URL and optional basic-auth credentials
• add opencode2 server add/list/remove management commands
• connect with opencode2 -r <name> or opencode2 --remote <name> while preserving -s for sessions and --server for raw URLs

Validation

• bun typecheck
• 19 focused CLI tests pass
• built the Linux x64 CLI and exercised the full saved-profile-to-TUI flow
• full CLI suite: 46 passed; the existing concurrent-service stress test hit a Bun SystemResources panic under host contention

Requested by: @R44VC0RP (Ryan Vogel via Slack)