Fix sitemap package URLs returning 404

Chi's {page} param in /sitemap-packages-{page}.xml captures "0.xml"
instead of just "0", causing strconv.Atoi to fail. Strip the .xml
suffix before parsing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: retlehs

internal/http/seo.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"net/http"
 	"strconv"
+	"strings"
 	"sync"
 	"time"
 
@@ -253,7 +254,8 @@ func handleSitemapPackages(a *app.App, data *sitemapData) http.HandlerFunc {
 			return
 		}
 
-		page, err := strconv.Atoi(chi.URLParam(r, "page"))
+		pageStr := strings.TrimSuffix(chi.URLParam(r, "page"), ".xml")
+		page, err := strconv.Atoi(pageStr)
 		if err != nil || page < 0 {
 			http.NotFound(w, r)
 			return