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/handlers_test.go

@@ -87,10 +87,11 @@ func TestRenderTemplate(t *testing.T) {
 			"Version": "1.0.0",
 		}
 
-		// When templates don't exist, renderTemplate should return an error
-		h.renderTemplate(w, req, []string{"nonexistent.html"}, data)
+		// When a non-existent template name is requested, renderTemplate
+		// should return an internal server error
+		h.renderTemplate(w, req, "nonexistent.html", data)
 
-		// Should return internal server error when template parsing fails
+		// Should return internal server error when template is not found
 		assert.Equal(t, http.StatusInternalServerError, w.Code)
 	})
 }