Enable language switching for guest users

Changes:
- Move locale.update route outside auth middleware
- Update LocaleController to support both authenticated and guest users
  - Guest users: Save locale preference to session only
  - Authenticated users: Save to both session and database
- Add language switcher dropdown to header for all users
  - Display current language with globe icon
  - Show all 8 supported languages in dropdown
  - Highlight currently selected language with checkmark

This allows non-logged-in users to change the interface language,
improving accessibility for international visitors.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/routes/web.php

@@ -22,11 +22,13 @@
     return view('dashboard');
 })->middleware(['auth', 'verified'])->name('dashboard');
 
+// Locale switcher - available for all users (both authenticated and guest)
+Route::post('/locale', [LocaleController::class, 'update'])->name('locale.update');
+
 Route::middleware('auth')->group(function () {
     Route::get('/profile', [ProfileController::class, 'edit'])->name('profile.edit');
     Route::patch('/profile', [ProfileController::class, 'update'])->name('profile.update');
     Route::delete('/profile', [ProfileController::class, 'destroy'])->name('profile.destroy');
-    Route::post('/locale', [LocaleController::class, 'update'])->name('locale.update');
 });
 
 // Admin routes