Add ESLint + pre-commit hook and fix the issues it surfaced

src/core/format-detection.ts

@@ -19,9 +19,7 @@ export interface FormatDetection {
 
 function isTopology(value: unknown): boolean {
   return (
-    typeof value === 'object' &&
-    value !== null &&
-    (value as { type?: unknown }).type === 'Topology'
+    typeof value === 'object' && value !== null && (value as { type?: unknown }).type === 'Topology'
   );
 }
 
@@ -32,7 +30,7 @@ export function detectFormat(raw: string): FormatDetection {
 
   // 1. Try JSON first — highest confidence signal.
   try {
-    const parsed = JSON.parse(text);
+    const parsed: unknown = JSON.parse(text);
     return {
       format: isTopology(parsed) ? 'topojson' : 'json',
       confidence: 'high',