Increase feed check parallelism for 1Gbps bandwidth

- Workers: 1000 -> 4000
- Work channel buffer: 1000 -> 4000
- Fetch batch size: 1000 -> 4000
- MaxIdleConns: 100 -> 2000

Should improve throughput from ~15 feeds/sec to ~50-60 feeds/sec.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

crawler.go

@@ -36,7 +36,7 @@ func NewCrawler(connString string) (*Crawler, error) {
 			KeepAlive: 30 * time.Second,
 		}).DialContext,
 		ForceAttemptHTTP2:     false,
-		MaxIdleConns:          100,
+		MaxIdleConns:          2000,
 		IdleConnTimeout:       90 * time.Second,
 		TLSHandshakeTimeout:   30 * time.Second,
 		ExpectContinueTimeout: 1 * time.Second,
@@ -161,10 +161,10 @@ func (c *Crawler) StartMaintenanceLoop() {
 
 // StartFeedCheckLoop runs the feed_check loop (checking feeds for new items)
 func (c *Crawler) StartFeedCheckLoop() {
-	numWorkers := 1000
+	numWorkers := 4000
 
 	// Buffered channel for feed work
-	workChan := make(chan *Feed, 1000)
+	workChan := make(chan *Feed, 4000)
 
 	// Start workers
 	for i := 0; i < numWorkers; i++ {
@@ -175,7 +175,7 @@ func (c *Crawler) StartFeedCheckLoop() {
 		}()
 	}
 
-	const fetchSize = 1000
+	const fetchSize = 4000
 	for {
 		if c.IsShuttingDown() {
 			close(workChan)