feat: rename subscription routes to /mana across all apps

- Add /mana route to chat web app with SubscriptionPage
- Add manaHref prop to PillNavigation for user dropdown link
- Add mana icon to PillDropdown component
- Rename /subscription to /mana in picture, manacore, and manadeck apps
- Update navigation items to use mana icon and label

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

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

apps/manadeck/apps/web/src/routes/(app)/+layout.svelte

@@ -25,7 +25,7 @@
 		{ href: '/decks', label: 'Decks', icon: 'archive' },
 		{ href: '/explore', label: 'Explore', icon: 'search' },
 		{ href: '/progress', label: 'Progress', icon: 'chart' },
-		{ href: '/subscription', label: 'Mana', icon: 'mana' },
+		{ href: '/mana', label: 'Mana', icon: 'mana' },
 		{ href: '/profile', label: 'Profile', icon: 'user' },
 	];