feat: combine TFL alerts into single feed item

TflSource.fetchItems() now returns one TflStatusFeedItem with an
alerts array instead of separate items per line disruption. Signals
use the highest severity. Alerts sorted by station distance.

Co-authored-by: Ona <no-reply@ona.com>

apps/aelis-backend/src/enhancement/llm-client.ts

@@ -4,7 +4,7 @@ import type { EnhancementResult } from "./schema.ts"
 
 import { enhancementResultJsonSchema, parseEnhancementResult } from "./schema.ts"
 
-const DEFAULT_MODEL = "z-ai/glm-4.7-flash"
+const DEFAULT_MODEL = "openai/gpt-4.1-mini"
 const DEFAULT_TIMEOUT_MS = 30_000
 
 export interface LlmClientConfig {