Fix dropAllData FK constraint violation on beacon deletion

[Copilot]

dropAllData was always failing with FOREIGN KEY constraint failed because the deletion order omitted several entity types that hold FK references to Beacon, Host, and Quest.

Missing deletions

Entity	FK references	Must precede
Notification	notification_event	Event
Event	beacon_events, host_events, quest_events	Beacon, Host, Quest
BeaconHistory	beacon_history_beacon	Beacon
ShellPivot	shell_id, portal_id, credential_id	Shell, Portal, HostCredential
Adventure	referenced by quest.adventure_id	— (add after Quest)
ScheduledTask	referenced by quest.scheduled_task_id	— (add after Quest)

Changes

• mutation.resolvers.go — inserts the six missing Delete() calls in topologically correct order within DropAllData
• testdata/mutations/dropAllData/WithEvents.yml — adds a regression test that seeds events, notifications, and beacon_histories before calling dropAllData, directly covering the reported failure path

[hulto]

@copilot run go generate ./tavern/... and commit the generated files

[Copilot]

@copilot run go generate ./tavern/... and commit the generated files

Ran go generate ./tavern/... — the working tree remained clean. Our changes were limited to the hand-written mutation.resolvers.go and a new YAML test fixture, neither of which affects generated files, so there's nothing new to commit.