feat: add Reset Stats button to admin LLM tracking panel

Allows resetting the LLM stats aggregation window without deleting
historical data. Stores a reset timestamp in metadata and filters
the aggregation query to only include calls after that point.

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

shared/dist/types.d.ts

@@ -393,4 +393,5 @@ export interface ClientEvents {
     'admin-toggle-llm-tracking': (data: {
         enabled: boolean;
     }) => void;
+    'admin-reset-llm-stats': () => void;
 }

shared/src/types.ts

@@ -382,4 +382,5 @@ export interface ClientEvents {
   'log-unsubscribe': () => void;
   'admin-llm-stats': () => void;
   'admin-toggle-llm-tracking': (data: { enabled: boolean }) => void;
+  'admin-reset-llm-stats': () => void;
 }