Fix blank page: URL types and inline style issues in templates

- Use template.URL for all URLs passed to templates (RSSURL, ImageURL)
- Pre-compute episode image URLs in handler as safe types
- Remove all inline style attributes, use CSS classes instead
- Add template error logging to catch silent failures
- HTML/template rejects raw strings in URL and CSS+URL contexts

handler/template.go

@@ -3,6 +3,7 @@ package handler
 import (
 	"html/template"
 	"io"
+	"log"
 )
 
 type Templates struct {
@@ -12,7 +13,8 @@ type Templates struct {
 func NewTemplates(tmpl *template.Template) *Templates {
 	return &Templates{tmpl: tmpl}
 }
-
 func (t *Templates) Render(w io.Writer, name string, data any) {
-	_ = t.tmpl.ExecuteTemplate(w, name+".html", data)
+	if err := t.tmpl.ExecuteTemplate(w, name+".html", data); err != nil {
+		log.Printf("template error: %s: %v", name, err)
+	}
 }