Unify sync triggers and move stall sync to hourly cadence

## Parent PRD

#1

## What to build

Create a shared trigger path for scheduled and manual stall sync, then move the automated stall freshness cadence to hourly while preserving the manual override. This slice should prove that the freshness SLA is operationally achievable without changing the public product surface.

## Acceptance criteria

- [ ] Scheduled and manual stall sync entry points invoke the same orchestration path.
- [ ] Production scheduling targets hourly stall sync execution.
- [ ] Manual sync remains available as an operator override and is covered by tests around observable trigger behavior.

## Blocked by

None - can start immediately.

## User stories addressed

Reference by number from the parent PRD:

- User story 1
- User story 12
- User story 13
- User story 14
- User story 30