Add listActions() and executeAction() to FeedSource for write
operations back to external services. Actions use arktype schemas
for input validation via StandardSchemaV1.
- ActionDefinition type with optional input schema
- FeedEngine routes actions with existence and ID validation
- Source IDs use reverse-domain format (aris.location, aris.tfl)
- LocationSource: update-location action with schema validation
- TflSource: set-lines-of-interest action with lineId validation
- No-op implementations for sources without actions
Co-authored-by: Ona <no-reply@ona.com>
