feat(issues): load all open issues without limit, paginate closed (#459)

- Add ListOpenIssues SQL query (excludes done/cancelled, no LIMIT)
- Add CountIssues SQL query for true total count
- Backend: support open_only=true param, fix total to return real count
- Frontend: two-phase fetch in issue store (all open + first 50 closed)
- Add fetchMoreClosed action for paginated closed issue loading
- Replace all hardcoded limit:200 with store.fetch() calls

Resolves MUL-369

Co-authored-by: Devv <devv@Devvs-Mac-mini.local>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/shared/api/client.ts

@@ -172,6 +172,7 @@ export class ApiClient {
     if (params?.status) search.set("status", params.status);
     if (params?.priority) search.set("priority", params.priority);
     if (params?.assignee_id) search.set("assignee_id", params.assignee_id);
+    if (params?.open_only) search.set("open_only", "true");
     return this.fetch(`/api/issues?${search}`);
   }