[Phase 4] Auto-sync Toggle

[ViRUS-0-0]

Description

Right now, once connected, the plugin always tries to sync automatically when an order comes in. Some organizers may want to review data before anything reaches HubSpot, or may be setting up the integration and not ready for live syncing yet.
Add a toggle on the HubSpot settings page for each event: "Sync automatically" (on/off). When off, new orders are logged as pending but no task is queued — the organizer syncs manually from the order detail page or the sync problems page.

Tasks

• Add an "Auto-sync enabled" yes/no field to HubSpotEventSettings
• Add a migration for the new field
• Add the toggle to the HubSpot settings page — on by default
• In the signal receiver ([Phase 4] Signal Wiring and Background Queueing #27), check this setting before queuing a task — if auto-sync is off, write a pending sync record but do not enqueue

Acceptance Criteria

• With auto-sync off, placing an order does not create anything in HubSpot automatically
• With auto-sync off, clicking "Sync now" on an order syncs it immediately
• Toggling auto-sync back on does not retroactively sync pending records — the recovery task ([Phase 4] Recovery Task for Failed and Incomplete Syncs #28) handles that
• The toggle is visible and saveable on the settings page

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