Add PebbleDB storage, domain tracking, and web dashboard

- Split main.go into separate files for better organization:
  crawler.go, domain.go, feed.go, parser.go, html.go, util.go
- Add PebbleDB for persistent storage of feeds and domains
- Store feeds with metadata: title, TTL, update frequency, ETag, etc.
- Track domains with crawl status (uncrawled/crawled/error)
- Normalize URLs by stripping scheme and www. prefix
- Add web dashboard on port 4321 with real-time stats:
  - Crawl progress with completion percentage
  - Feed counts by type (RSS/Atom)
  - Top TLDs and domains by feed count
  - Recent feeds table
- Filter out comment feeds from results

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

util.go

@@ -0,0 +1,82 @@
+package main
+
+import (
+	"net/url"
+	"strings"
+)
+
+// normalizeURL strips scheme (http/https) and www. prefix to save storage space.
+// The normalized URL can be reconstructed with https:// for fetching.
+func normalizeURL(rawURL string) string {
+	// Remove scheme
+	u := rawURL
+	if strings.HasPrefix(u, "https://") {
+		u = u[8:]
+	} else if strings.HasPrefix(u, "http://") {
+		u = u[7:]
+	}
+
+	// Remove www. prefix
+	if strings.HasPrefix(u, "www.") {
+		u = u[4:]
+	}
+
+	return u
+}
+
+// normalizeHost strips www. prefix from a hostname for canonical storage
+func normalizeHost(host string) string {
+	if strings.HasPrefix(host, "www.") {
+		return host[4:]
+	}
+	return host
+}
+
+// reverseHost converts a reverse domain notation back to normal
+// e.g., "com.example.www" -> "www.example.com"
+func reverseHost(reverseHost string) string {
+	parts := strings.Split(reverseHost, ".")
+	for i, j := 0, len(parts)-1; i < j; i, j = i+1, j-1 {
+		parts[i], parts[j] = parts[j], parts[i]
+	}
+	return strings.Join(parts, ".")
+}
+
+// getTLD extracts the TLD from a hostname
+func getTLD(host string) string {
+	parts := strings.Split(host, ".")
+	if len(parts) > 0 {
+		return parts[len(parts)-1]
+	}
+	return ""
+}
+
+// makeAbsoluteURL resolves a relative URL against a base URL
+func makeAbsoluteURL(href, baseURL string) string {
+	base, err := url.Parse(baseURL)
+	if err != nil {
+		return href
+	}
+
+	link, err := url.Parse(href)
+	if err != nil {
+		return href
+	}
+
+	return base.ResolveReference(link).String()
+}
+
+// shouldCrawl checks if a link should be crawled (same host as base)
+func shouldCrawl(link, baseURL string) bool {
+	linkURL, err := url.Parse(link)
+	if err != nil {
+		return false
+	}
+
+	baseURLParsed, err := url.Parse(baseURL)
+	if err != nil {
+		return false
+	}
+
+	return linkURL.Host == baseURLParsed.Host
+}