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/fs.ts

@@ -70,7 +70,7 @@ function matchEtag(etag: string, header: string): boolean {
     if (t.startsWith("W/")) t = t.substring(2);
     try {
       t = JSON.parse(t);
-    } catch (e) {
+    } catch {
       // Ignore
     }
     if (t === "*") return true;