Migrate flow trigger enable modal to the conditions CRUD panel

What does this MR do and why?

Follow-up to !248807 (merged), which moved the flow trigger settings form to the FlowTriggerConditions CRUD panel but left the catalog Enable modal on the old multi-select FlowTriggerEventsField. That left the same event-configuration flow presented two different ways, which was the open thread deferred in that MR as a design question rather than a cleanup.

This MR switches the modal to FlowTriggerConditions so both surfaces share one UI:

• The panel owns its own validity ("at least one condition, no open form, all configs valid") and emits it, so the modal now gates submit on that single signal instead of a separate empty-list check.
• Dropped the modal's standalone trigger description text now that the panel carries its own title and description.
• Added top padding and a stable id to the consumer disclaimer paragraph below the panel.
• FlowTriggerEventsField has no remaining consumer, so it and its spec are removed (this also closes the dead-code request from the original MR, which was only deferred because the modal still used it).

References

• Original MR: !248807 (merged)
• Deferred design question: !248807 (comment 3650121930)
• Deferred dead-code removal: !248807 (comment 3650174586)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. In a project where Duo features are enabled, open the AI catalog and find a flow you can enable.
2. Select Enable to open the consumer modal.
3. Confirm the trigger section now renders the Conditions CRUD panel (matching Automate > Triggers > New trigger) instead of the old multi-select, with Add condition adding one condition at a time.
4. Confirm the default conditions (mention, assign, assign reviewer) are pre-selected.
5. Remove all conditions and confirm the modal blocks submit and the panel explains why.
6. Leave an Add condition form open and submit; confirm it blocks until the condition is finished or cancelled.
7. Enable with a valid set and confirm the emitted payload is unchanged (triggerTypes, and triggerFilter only when non-empty).
8. Confirm the disclaimer paragraph below the panel has spacing above it and is not flush against the form.

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