feat: remove OTP gate from transactions, fix categories auth, add implementation plan

- Remove OtpGateGuard from transactions controller (OTP verified at login)
- Fix categories controller to use authenticated user instead of TEMP_USER_ID
- Add comprehensive implementation plan document
- Update .env.example with WEB_APP_URL
- Prepare for admin dashboard development

apps/web/src/components/ThemeProvider.tsx

@@ -9,12 +9,17 @@ type ThemeProviderProps = {
 
 export function ThemeProvider({
   children,
-  defaultTheme = 'system',
+  defaultTheme = 'light',
   storageKey = 'tabungin-ui-theme',
 }: ThemeProviderProps) {
-  const [theme, setTheme] = useState<Theme>(
-    () => (localStorage.getItem(storageKey) as Theme) || defaultTheme
-  )
+  const [theme, setTheme] = useState<Theme>(() => {
+    const stored = localStorage.getItem(storageKey) as Theme
+    // If system theme is stored, convert to light
+    if (stored === 'system') {
+      return 'light'
+    }
+    return stored || defaultTheme
+  })
 
   const [actualTheme, setActualTheme] = useState<'dark' | 'light'>('light')
 
@@ -23,19 +28,10 @@ export function ThemeProvider({
 
     root.classList.remove('light', 'dark')
 
-    if (theme === 'system') {
-      const systemTheme = window.matchMedia('(prefers-color-scheme: dark)')
-        .matches
-        ? 'dark'
-        : 'light'
-
-      root.classList.add(systemTheme)
-      setActualTheme(systemTheme)
-      return
-    }
-
-    root.classList.add(theme)
-    setActualTheme(theme)
+    // Only support light and dark, no system
+    const themeToApply = theme === 'system' ? 'light' : theme
+    root.classList.add(themeToApply)
+    setActualTheme(themeToApply)
   }, [theme])
 
   const value = {