feat(workbuddy): align account forms and add check-in defaults

[caigee-cmd]

Summary

• Align create-account and edit-account form fields (labels, NumberField, spacing) so WorkBuddy advanced settings no longer look uneven.
• Add a system-wide WorkBuddy daily check-in default on the System page; new accounts inherit it, and each WorkBuddy account can override it on edit.
• Keep the scheduler keyed off each account's own time, with the existing 21:00 retry behavior.

Test plan

• go test ./internal/accounts ./internal/api -count=1
• cd frontend && npm run lint && npm run sync
• Open System settings, change WorkBuddy check-in default, reopen Add Account and confirm the advanced time field seeds from it
• Create a WorkBuddy account with auto check-in on and a custom time; confirm the account card shows that time
• Edit the same account and change the check-in time; confirm PATCH persists and the card updates
• Confirm non-WorkBuddy accounts do not show the check-in time field in edit