#18830: fix(slack): account for HTTP mode in isConfigured check(#7634)

## Summary - `isConfigured` and `describeAccount.configured` previously required both `botToken` and `appToken`, which meant Slack accounts using HTTP mode were never considered configured - Updated the condition to accept either `appToken` (socket mode) or `config.mode === "http"` as valid configurations alongside `botToken` ## Test plan - [ ] Verify a Slack account in HTTP mode (no `appToken`) is reported as configured - [ ] Verify a Slack account in socket mode still requires both `botToken` and `appToken` - [ ] Verify `describeAccount` returns `configured: true` for HTTP mode accounts fix issue #7634 🤖 Generated with [Claude Code](https://claude.com/claude-code)