feat(ui): project drill-down route with repo-filtered event timeline

Add repo filter param to /v1/events (SQL COALESCE across payload
shapes per source). New /project/:source/* route renders a filtered
activity timeline for a single repo. Dashboard cards link to the
drill-down page.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/api/client.ts

@@ -69,6 +69,7 @@ export interface EventQuery {
   from?: Date;
   to?: Date;
   sources?: Source[];
+  repo?: string;
   limit?: number;
 }
 
@@ -81,6 +82,7 @@ export async function fetchEvents(q: EventQuery): Promise<TimelineItem[]> {
   if (q.sources && q.sources.length > 0) {
     params.set('source', q.sources.join(','));
   }
+  if (q.repo) params.set('repo', q.repo);
   if (q.limit) params.set('limit', String(q.limit));
 
   const resp = await fetch(`${API_BASE}/events?${params}`);