fix: template rendering returns empty pages (closes #18)

Reorder template.ParseFS arguments so the page template file is listed
first. Go's template package names the template set after the first file
parsed. When htmlheader.html was first, its content (entirely a
{{define}} block) became the root template, which is empty. By putting
the page file first, its {{template "base" .}} invocation becomes the
root action and the page renders correctly.

internal/handlers/handlers.go

@@ -37,9 +37,13 @@ type Handlers struct {
 
 // parsePageTemplate parses a page-specific template set from the embedded FS.
 // Each page template is combined with the shared base, htmlheader, and navbar templates.
+// The page file must be listed first so that its root action ({{template "base" .}})
+// becomes the template set's entry point. If a shared partial (e.g. htmlheader.html)
+// is listed first, its {{define}} block becomes the root — which is empty — and
+// Execute() produces no output.
 func parsePageTemplate(pageFile string) *template.Template {
 	return template.Must(
-		template.ParseFS(templates.Templates, "htmlheader.html", "navbar.html", "base.html", pageFile),
+		template.ParseFS(templates.Templates, pageFile, "base.html", "htmlheader.html", "navbar.html"),
 	)
 }