feat(fase-10): sidebar "+ New collective" entry + modal (10.6)

Adds a new "+ New collective" entry at the bottom of the sidebar
collective-switcher dropdown (and the mobile drawer for parity).
Clicking it opens a CreateCollectiveModal that reuses the same
onboarding form — name + emoji grid — and calls the existing
create_collective() RPC (migration 012). On success, the new
collective is appended to $userCollectives, set active in
$currentCollective, persisted to localStorage, and the user is sent
to /lists.

Side effects:
- Switcher now opens even with a single collective (previously gated
  on >1) so the entry is always reachable; the chevron is always
  shown.
- DesktopSidebar gets a data-testid on the switcher button so the
  Playwright suite can target it without text matching.

O-04 (rescued from Fase 7): Eva creates her first collective via
onboarding, then opens the switcher and creates a second one without
leaving /lists; both collectives end up in the switcher and the DB.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/web/src/lib/components/layout/MobileDrawer.svelte

@@ -2,9 +2,12 @@
 	import { currentCollective, userCollectives } from '$lib/stores/collective';
 	import { displayName } from '$lib/stores/auth';
 	import Avatar from '$lib/components/Avatar.svelte';
+	import CreateCollectiveModal from '$lib/components/CreateCollectiveModal.svelte';
 	import { logout } from '$lib/auth';
 	import * as m from '$lib/paraglide/messages';
-	import { Settings, Users, LogOut, X } from 'lucide-svelte';
+	import { Settings, Users, LogOut, X, Plus } from 'lucide-svelte';
+
+	let showCreate = $state(false);
 
 	let { open = $bindable(false) }: { open?: boolean } = $props();
 
@@ -65,10 +68,21 @@
 					</button>
 				{/each}
 			</div>
+			<button
+				type="button"
+				onclick={() => {
+					close();
+					showCreate = true;
+				}}
+				class="mt-2 flex w-full items-center gap-2 rounded-md px-2 py-2 text-left text-sm text-text-secondary hover:bg-black/5 dark:hover:bg-white/5"
+			>
+				<Plus size={14} strokeWidth={1.5} />
+				{m.sidebar_create_collective()}
+			</button>
 			<a
 				href="/collective/manage"
 				onclick={close}
-				class="mt-2 flex items-center gap-2 rounded-md px-2 py-2 text-sm text-text-secondary hover:bg-black/5 dark:hover:bg-white/5"
+				class="mt-1 flex items-center gap-2 rounded-md px-2 py-2 text-sm text-text-secondary hover:bg-black/5 dark:hover:bg-white/5"
 			>
 				<Users size={14} strokeWidth={1.5} />
 				{m.manage_title()}
@@ -106,3 +120,7 @@
 		</div>
 	</aside>
 {/if}
+
+{#if showCreate}
+	<CreateCollectiveModal onClose={() => (showCreate = false)} />
+{/if}