Adds 7 new composable Query modules following the existing
DeviceQuery/AlertQuery pattern. Each exposes base/0 and for_organization/1,2
plus filters used by 2+ callers.
New modules:
- Towerops.OnCall.ScheduleQuery
- Towerops.OnCall.EscalationPolicyQuery
- Towerops.Maintenance.MaintenanceWindowQuery
- Towerops.Organizations.MembershipQuery
- Towerops.Organizations.InvitationQuery
- Towerops.Agents.AgentTokenQuery
- Towerops.Gaiia.DeviceSubscriberLinkQuery
Refactors callsites in alerts, agents, devices, gaiia, maintenance, on_call,
organizations, search, and subscription_limits to use existing or new Query
modules instead of inline 'where: x.organization_id == ^...' clauses.