build: migrate eslint to v10 flat config and upgrade typescript

Replace .eslintrc.json with eslint.config.js using the new flat config
format required by ESLint 10. Swap @typescript-eslint/eslint-plugin and
@typescript-eslint/parser for the unified typescript-eslint package.
Upgrade TypeScript to 5.9 and @types/node to 25. Apply automatic code
fixes: remove unused catch bindings and preserve error cause in auth
header parsing.

lib/cwmp/db.ts

@@ -78,7 +78,7 @@ export async function fetchDevice(
 
     try {
       res.push([Path.parse(path), t, attrs]);
-    } catch (err) {
+    } catch {
       // The path parser is now more strict so we might be in a situation where
       // the database contains invalid paths from before this change So here we
       // encode the invalid characters.