feat(appointments): default Create Talk room on for new configs

[whoalin1]

Summary

New appointment schedules left createTalkRoom unset (falsy), so the “Create a Talk room” checkbox started unchecked and users had to opt in every time.

AppointmentConfig.createDefault() now sets createTalkRoom: true so Talk rooms are opt-out. Users can still uncheck the box. Existing configs are unchanged. When Talk is not available, AppointmentConfigModal already forces the option off.

Closes #5774

Test plan

• With Talk enabled: open Appointments → create a new schedule → “Create a Talk room” is checked by default
• Uncheck the box, save → no Talk room created for bookings on that schedule
• With Talk disabled/unavailable: new schedule still opens; Talk option stays off (modal clears it)
• Edit an existing schedule that had Talk off → checkbox remains off (defaults only apply to createDefault)

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AI disclosure

This PR was drafted with the help of AI coding assistants (Cursor agents / LLM-based tools), including the description. I am responsible for it and happy to rework anything that doesn't fit.

The commits don't carry Assisted-by: trailers yet; I can add them if wanted (that needs a force push).

[GVodyanov]

Looks good!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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Needs further consideration