Address review feedback on shared head template

- Fail fast (log.Fatalf) when shared templates fail to load, since all
  themes depend on _head being available
- Seed site_url with https://www.example.com instead of empty string,
  so OG/structured data URLs are always absolute
- Fall back to "index, follow" when robots_tag value is empty, not just
  when the setting key is missing

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

Author: compscidr

goblog.go

@@ -377,8 +377,7 @@ func main() {
 		// Load shared templates first, then theme templates
 		tmpl, err := template.New("").Funcs(funcMap).ParseGlob("templates/shared/*.html")
 		if err != nil {
-			log.Printf("Warning: failed to load shared templates: %v", err)
-			tmpl = template.New("").Funcs(funcMap)
+			log.Fatalf("Failed to load shared templates: %v", err)
 		}
 		tmpl, err = tmpl.ParseGlob(themePath + "templates/*.html")
 		if err != nil {

templates/shared/_head.html

@@ -6,7 +6,7 @@
   <meta name="keywords" content="{{ .settings.site_title.Value }}{{range .post.Tags}}, {{.Name}}{{end}}">
   <meta name="author" content="{{ .settings.site_title.Value }}">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
-  <meta name="robots" content="{{ with index .settings "robots_tag" }}{{ .Value }}{{ else }}index, follow{{ end }}" />
+  <meta name="robots" content="{{ with index .settings "robots_tag" }}{{ if .Value }}{{ .Value }}{{ else }}index, follow{{ end }}{{ else }}index, follow{{ end }}" />
   <meta property="og:site_name" content="{{ .settings.site_title.Value }}">
   {{ if .post }}
   <meta name="description" content="{{ .post.PlainTextPreview 155 }}">

tools/migrate.go

@@ -277,7 +277,7 @@ func seedDefaultSettings(db *gorm.DB) {
 		{Key: "custom_footer_code", Type: "textarea", Value: ""},
 		{Key: "theme", Type: "text", Value: "default"},
 		{Key: "robots_tag", Type: "text", Value: "index, follow"},
-		{Key: "site_url", Type: "text", Value: ""},
+		{Key: "site_url", Type: "text", Value: "https://www.example.com"},
 	}
 	for _, s := range defaults {
 		db.Where("key = ?", s.Key).FirstOrCreate(&s)