Add AT Protocol publishing, media support, and SQLite stability

Publishing:
- Add publisher.go for posting feed items to AT Protocol PDS
- Support deterministic rkeys from SHA256(guid + discoveredAt)
- Handle multiple URLs in posts with facets for each link
- Image embed support (app.bsky.embed.images) for up to 4 images
- External embed with thumbnail fallback
- Podcast/audio enclosure URLs included in post text

Media extraction:
- Parse RSS enclosures (audio, video, images)
- Extract Media RSS content and thumbnails
- Extract images from HTML content in descriptions
- Store enclosure and imageUrls in items table

SQLite stability improvements:
- Add synchronous=NORMAL and wal_autocheckpoint pragmas
- Connection pool tuning (idle conns, max lifetime)
- Periodic WAL checkpoint every 5 minutes
- Hourly integrity checks with PRAGMA quick_check
- Daily hot backup via VACUUM INTO
- Docker stop_grace_period: 30s for graceful shutdown

Dashboard:
- Feed publishing UI and API endpoints
- Account creation with invite codes

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

main.go

@@ -3,6 +3,8 @@ package main
 import (
 	"fmt"
 	"os"
+	"os/signal"
+	"syscall"
 )
 
 func main() {
@@ -17,7 +19,10 @@ func main() {
 		fmt.Fprintf(os.Stderr, "Error initializing crawler: %v\n", err)
 		os.Exit(1)
 	}
-	defer crawler.Close()
+
+	// Setup graceful shutdown
+	sigChan := make(chan os.Signal, 1)
+	signal.Notify(sigChan, syscall.SIGINT, syscall.SIGTERM)
 
 	// Start dashboard in background
 	go func() {
@@ -41,9 +46,24 @@ func main() {
 	// Stats loop (background) - updates once per minute
 	go crawler.StartStatsLoop()
 
-	// Cleanup loop (background) - removes old items once per hour
+	// Cleanup loop (background) - removes old items once per week
 	go crawler.StartCleanupLoop()
 
-	// Crawl loop (foreground - blocks forever)
-	crawler.StartCrawlLoop()
+	// Maintenance loop (background) - WAL checkpoints and integrity checks
+	go crawler.StartMaintenanceLoop()
+
+	// Crawl loop (background)
+	go crawler.StartCrawlLoop()
+
+	// Wait for shutdown signal
+	sig := <-sigChan
+	fmt.Printf("\nReceived %v, shutting down gracefully...\n", sig)
+
+	// Close crawler (checkpoints WAL and closes database)
+	if err := crawler.Close(); err != nil {
+		fmt.Fprintf(os.Stderr, "Error closing crawler: %v\n", err)
+		os.Exit(1)
+	}
+
+	fmt.Println("Shutdown complete")
 }