fix(frontend): resolve linting errors and component duplication

frontend/src/components/Footer.tsx

@@ -0,0 +1,13 @@
+import React from 'react';
+
+const Footer: React.FC = () => {
+  return (
+    <footer className="py-4 text-center">
+      <p className="text-xs text-slate-500">
+        v{__APP_VERSION__} ({__APP_GITSHA__})
+      </p>
+    </footer>
+  );
+};
+
+export default Footer;

frontend/src/components/stats/DailySummary.tsx

@@ -100,8 +100,8 @@ const DailySummary: React.FC<DailySummaryProps> = ({ from_date, to_date, day_sta
              width={60}
            />
           <Tooltip
-              formatter={(value: any, name: any) => [
-                formatMinutes(Math.round(Number(value ?? 0) * 60)),
+              formatter={(value: number | string | readonly (string | number)[] | undefined, name: string | number | undefined) => [
+                formatMinutes(Math.round(Number((Array.isArray(value) ? value[0] : value ?? 0) * 60))),
                 name === 'daySleep' ? 'Day' : 'Night',
               ]}
           />

frontend/src/components/stats/SleepTimetable.tsx

@@ -52,7 +52,8 @@ const Timetable = ({ from_date, to_date, day_start, day_end }: TimetableProps) =
 
   useEffect(() => {
     if (days.length > 0) {
-      setSelectedDayIndex(days.length - 1);
+      const newIndex = days.length - 1;
+      setSelectedDayIndex(prev => (prev !== newIndex ? newIndex : prev));
     }
   }, [days]);
 

frontend/src/hooks/SettingsProvider.tsx

@@ -1,4 +1,4 @@
-import React, { createContext, useContext, useState, useEffect, ReactNode } from 'react';
+import { createContext, useState, useEffect, ReactNode } from 'react';
 
 const STORAGE_KEY = 'baby-sleep-settings';
 

frontend/src/hooks/useSettings.ts

@@ -1,5 +1,5 @@
 import { useContext } from 'react';
-import { SettingsContext, Settings } from './SettingsProvider';
+import { SettingsContext } from './SettingsProvider';
 
 export function useSettings() {
   const context = useContext(SettingsContext);

frontend/vite.config.ts

@@ -3,9 +3,16 @@ import react from '@vitejs/plugin-react'
 import tailwindcss from '@tailwindcss/vite'
 import path from 'path'
 
+const APP_VERSION = process.env.VITE_APP_VERSION || 'unknown';
+const APP_GITSHA = process.env.VITE_APP_GITSHA || 'unknown';
+
 export default defineConfig({
   base: './',
   plugins: [react(), tailwindcss()],
+  define: {
+    __APP_VERSION__: JSON.stringify(APP_VERSION),
+    __APP_GITSHA__: JSON.stringify(APP_GITSHA),
+  },
   resolve: {
     alias: {
       '@': path.resolve(__dirname, './src'),