feat: add actions to FeedSource interface

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>

packages/aris-core/package.json

@@ -6,5 +6,8 @@
 	"types": "src/index.ts",
 	"scripts": {
 		"test": "bun test ."
+	},
+	"dependencies": {
+		"@standard-schema/spec": "^1.1.0"
 	}
 }