Add stage 4: frontend lists view + enforce 100-list cap

API: GET /api/lists is now ordered alphabetically (COLLATE NOCASE) by title
with no other option, and TodoListController rejects a create past 100 lists
per owner with 409. New TodoListRepository::countForOwner.

Frontend: HomeView replaces the placeholder with the user's lists (rendered in
API order) and a create form (title + optional description). New Pinia lists
store fetches and creates, re-fetching after a create so the new list sorts
into place; it is reset on logout. Form disables and explains at 100 lists;
create errors surface inline. Neutral .badge with a .badge--warn variant;
dropped the unused .facts styles.

Tests: alphabetical ordering and the 100-list cap. Suite: 17 passing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/App.vue

@@ -1,12 +1,15 @@
 <script setup lang="ts">
 import { RouterView, useRouter } from 'vue-router'
 import { useAuthStore } from './stores/auth'
+import { useListsStore } from './stores/lists'
 
 const auth = useAuthStore()
+const lists = useListsStore()
 const router = useRouter()
 
 async function onLogout() {
   auth.logout()
+  lists.reset()
   await router.push({ name: 'login' })
 }
 </script>