feat: Pattern Lab Discover + fix history run display

Fix: history runs now always show results — create synthetic selected preset
from run data when no matching preset found (was broken for custom events).
Also force mode='events' and reset matchResults on history load.

Discover tab: new "Discover" panel in left sidebar (AI knowledge search).
- GPT-4o generates 6 matching events from a free-text query (date, assets, hint)
- Confidence score + category badge per event
- Click → pre-fills experiment form exactly like a preset → ready to Run
- Backend: POST /api/pattern-lab/discover (DiscoverRequest, sorted by confidence)
- Frontend: useDiscoverEvents hook + DiscoveredEvent type + Discover UI with
  Enter-to-search, spinner, empty states

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/hooks/useApi.ts

@@ -1036,6 +1036,17 @@ export const useFindMatchingPattern = () =>
       api.post('/pattern-lab/find-matching', body).then(r => r.data),
   })
 
+export type DiscoveredEvent = {
+  label: string; date: string; category: string; horizon_days: number
+  assets: string[]; hint: string; confidence: number
+}
+
+export const useDiscoverEvents = () =>
+  useMutation({
+    mutationFn: (body: { query: string; n?: number }): Promise<{ events: DiscoveredEvent[]; source: string; query: string }> =>
+      api.post('/pattern-lab/discover', body).then(r => r.data),
+  })
+
 export const useDeleteLabRun = () => {
   const qc = useQueryClient()
   return useMutation({