fix: Sync custom targeting keys to adapter_config during inventory sync

[BaiyuScope3]

Problem

Erin had issue when approving a media buy for GAM , error message

Media buy approved but adapter creation failed: Adapter creation failed: AXE include key 'axei' not found in GAM. Create the custom targeting key in GAM UI and sync using 'Sync Custom Targeting Keys' button.

Event after the targeting key updated in the GAM IU, still showing the same error.

The root cause is below:
When clicking 'Sync Targeting Data' in the Targeting Browser:

1. Keys are written to gam_inventory table (for UI display) ✅
2. But adapter_config.custom_targeting_keys column is NOT updated ❌
3. Media Buy approval calls GAMTargetingManager.resolve_custom_targeting_key_id() which reads from adapter_config.custom_targeting_keys
4. Result: "AXE include key 'axei' not found in GAM" error even though keys exist

Solution

After writing custom targeting keys to gam_inventory, also update adapter_config.custom_targeting_keys with the key name → GAM ID mapping.

Changes

• Added _update_adapter_config_targeting_keys() method to gam_inventory_service.py
• Called the method in background_sync_service.py after writing targeting keys to database

Testing

• All existing unit tests pass
• Imports verified working
• Manual testing: Click 'Sync Targeting Data' → adapter_config.custom_targeting_keys should now be populated