[Fix] Discord setup shows installation controls when user links account

[roomote-roomote]

Created by Roomote. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Replaced installation diagnostics in the configured Discord onboarding state with a focused personal account-linking step.
• Added the step title "Link Discord Account" while preserving the existing Continue gate until the user's Discord identity is linked.
• Added focused coverage for users who arrive with Discord already configured and for the transition immediately after saving credentials.

Why this change was made

Users prompted to link their personal Discord account were shown workspace-level installation diagnostics and admin actions, obscuring the task they needed to complete.

Impact

Configured Discord onboarding now matches the focused account-linking experience used by other entry points, while Discord installation diagnostics remain available in Settings. Browser proof could not reach the configured state without valid local Discord bot credentials; the configured and post-save states are covered by the focused component tests.

[roomote-community]

No code issues found. See task

_{Reviewed adb6386}