feat(FN-2387): unify agents view loading through useAgents

- Move AgentsView to consume agents, loading state, and reload logic directly from useAgents
- Extend useAgents with filterState/showSystemAgents options and always pass includeEphemeral in fetch filters
- Remove duplicate initial fetch/SSE path in AgentsView and rely on hook-managed refresh behavior
- Add regression coverage for single initial load and system-agent visibility toggling behavior
- Update useAgents hook tests to assert the new includeEphemeral fetch contract

packages/core/vitest.config.ts

@@ -2,7 +2,10 @@ import { defineConfig } from "vitest/config";
 import { resolve } from "node:path";
 import { cpus } from "node:os";
 
-const defaultMaxWorkers = Math.max(1, cpus().length - 1);
+// Keep worker fan-out conservative by default. Over-subscribing threads can
+// starve Vitest's worker RPC channel and trigger flaky "onTaskUpdate" timeouts
+// under heavy SQLite test load.
+const defaultMaxWorkers = Math.min(4, Math.max(1, cpus().length - 1));
 const requestedMaxWorkers = Number.parseInt(process.env.VITEST_MAX_WORKERS ?? String(defaultMaxWorkers), 10);
 const maxWorkers = Math.max(1, Number.isFinite(requestedMaxWorkers) ? requestedMaxWorkers : defaultMaxWorkers);
 process.env.VITEST_MAX_WORKERS = String(maxWorkers);