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

src/app/infrastructure/db.ts

@@ -56,8 +56,9 @@ function tx<T>(
         const transaction = db.transaction(store, mode);
         const request = run(transaction.objectStore(store));
         transaction.oncomplete = () => resolve(request.result);
-        transaction.onerror = () => reject(transaction.error);
-        transaction.onabort = () => reject(transaction.error);
+        const fail = () => reject(transaction.error ?? new Error('IndexedDB transaction failed'));
+        transaction.onerror = fail;
+        transaction.onabort = fail;
       }),
   );
 }
@@ -69,10 +70,10 @@ export const getAll = <T>(store: string): Promise<T[]> =>
   tx<T[]>(store, 'readonly', (s) => s.getAll() as IDBRequest<T[]>);
 
 export const put = <T>(store: string, value: T): Promise<IDBValidKey> =>
-  tx<IDBValidKey>(store, 'readwrite', (s) => s.put(value as unknown as Record<string, unknown>));
+  tx<IDBValidKey>(store, 'readwrite', (s) => s.put(value));
 
 export const del = (store: string, key: IDBValidKey): Promise<undefined> =>
-  tx<undefined>(store, 'readwrite', (s) => s.delete(key) as IDBRequest<undefined>);
+  tx<undefined>(store, 'readwrite', (s) => s.delete(key));
 
 /** Test-only: forget the memoized connection so a fresh `openDB` reopens. */
 export function _resetDbForTests(): void {

src/app/infrastructure/settings-store.test.ts

@@ -71,7 +71,11 @@ describe('settings-store · ui.theme', () => {
 
       saveUiTheme('dark');
 
-      const stored = JSON.parse(localStorage.getItem(KEY)!);
+      const stored = JSON.parse(localStorage.getItem(KEY)!) as {
+        version: number;
+        ui: { theme: string; previewFitMode: string };
+        editor: { fontSize: number };
+      };
       expect(stored.ui.theme).toBe('dark');
       // Everything else survives — nothing clobbered.
       expect(stored.version).toBe(1);

src/app/infrastructure/settings-store.ts

@@ -40,7 +40,7 @@ function readRaw(): StoredSettings {
   try {
     const raw = localStorage.getItem(KEY);
     if (!raw) return {};
-    const parsed = JSON.parse(raw);
+    const parsed: unknown = JSON.parse(raw);
     return parsed && typeof parsed === 'object' ? (parsed as StoredSettings) : {};
   } catch (err) {
     console.warn('[settings] failed to read, using defaults', err);