refactor: use go:embed for templates

Templates are now embedded using //go:embed and parsed once at startup
with template.Must(template.ParseFS(...)). This avoids re-parsing
template files from disk on every request and removes the dependency
on template files being present at runtime.

closes #7

internal/handlers/index.go

@@ -34,7 +34,7 @@ func (s *Handlers) HandleIndex() http.HandlerFunc {
 		}
 
 		// Render the template
-		s.renderTemplate(w, req, []string{"templates/base.html", "templates/index.html"}, data)
+		s.renderTemplate(w, req, "index.html", data)
 	}
 }