feat(editor): integrate Monaco Editor for local file editing and enhance language inference

surfsense_web/lib/editor-language.ts

@@ -0,0 +1,34 @@
+const EXTENSION_TO_MONACO_LANGUAGE: Record<string, string> = {
+	css: "css",
+	csv: "plaintext",
+	cjs: "javascript",
+	html: "html",
+	htm: "html",
+	ini: "ini",
+	js: "javascript",
+	json: "json",
+	markdown: "markdown",
+	md: "markdown",
+	mjs: "javascript",
+	py: "python",
+	sql: "sql",
+	toml: "plaintext",
+	ts: "typescript",
+	tsx: "typescript",
+	xml: "xml",
+	yaml: "yaml",
+	yml: "yaml",
+};
+
+export function inferMonacoLanguageFromPath(filePath: string | null | undefined): string {
+	if (!filePath) return "plaintext";
+
+	const fileName = filePath.split("/").pop() ?? filePath;
+	const extensionIndex = fileName.lastIndexOf(".");
+	if (extensionIndex <= 0 || extensionIndex === fileName.length - 1) {
+		return "plaintext";
+	}
+
+	const extension = fileName.slice(extensionIndex + 1).toLowerCase();
+	return EXTENSION_TO_MONACO_LANGUAGE[extension] ?? "plaintext";
+}