Disable Save button and show spinner during Agreement/Action creation/update

[jhodapp]

Description

Prevents duplicate Agreements and Actions from being created or updated when the Save/Update button is clicked multiple times during backend latency. The Save/Update button is now disabled with a spinner while the mutation is in flight. Failed operations now display a user-facing error toast via sonner.

GitHub Issue: Fixes #281

Changes

• Wired existing isLoading state from useAgreementMutation and useActionMutation hooks through CoachingTabsContainer to both list components as isSaving prop
• Added Loader2 spinner icon and disabled state to Save/Update buttons in both AgreementsList and ActionsList
• Guarded Enter key submission to prevent duplicate saves while a mutation is in flight
• Added toast.error() notifications for failed save, update, and delete operations on both Agreements and Actions (including the completion toggle checkbox)
• Replaced silent throw err re-throws with user-facing toast messages
• Updated 5 test files to include the new isSaving prop in mockProps
• Added 7 new tests verifying error toasts appear on each failure path

Screenshots / Videos Showing UI Changes (if applicable)

None, trivial chanages

Testing Strategy

• All 447 unit tests pass
• Production build succeeds
• Manual testing: create an Agreement or Action and verify the button shows a spinner and is disabled during save
• Manual testing: simulate a backend failure and verify an error toast appears

Concerns

• None — this wires up existing infrastructure (isLoading from useEntityMutation) that was already being tracked but not surfaced to the UI. The toast uses the same sonner pattern already established across the codebase.