feat(fase-15): exclude-on-list wiring + CI-02 e2e (15.4)

/lists/[id]/+page.svelte now passes the current item names through to
fetchSuggestions as excludeNames, both on initial cold-load and on every
debounced keystroke. The exclude list is a `$derived` of `items` so it
recomputes the moment an optimistic insert lands — the next keystroke
no longer surfaces the freshly-added item.

ItemSuggestions.svelte gets a stable data-testid handle on the strip
plus per-chip testids so the suite can assert presence/absence without
fragile text matches. The component still hides itself entirely when
the post-filter suggestion list is empty (the dropdown was already
gated on `suggestions.length > 0`).

Playwright CI-02 lives on a freshly-created list (the seed list is
shared with the entire suite and tends to accumulate hundreds of test
items, which both buries the assertion target and inflates the
excludeNames URL). Boosts two synthetic names heavily so they lead
the dropdown regardless of pollution in item_frequency, verifies
"added" → "next fetch excludes it", and tears its own rows down via
the admin purge RPC (direct table deletes are blocked by the deny-all
RLS from migration 006).

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

apps/web/src/routes/(app)/lists/[id]/+page.svelte

@@ -309,7 +309,12 @@
 		loading = false;
 
 		if ($currentCollective) {
-			suggestions = await fetchSuggestions($currentCollective.id, '');
+			// Fase 15: exclude items already on the list from the suggestion
+			// strip — the user doesn't need to be nudged to re-add what's
+			// already there.
+			suggestions = await fetchSuggestions($currentCollective.id, '', {
+				excludeNames: items.map((i) => i.name)
+			});
 			// Load tags for this collective — picker + filter need them.
 			await loadTags($currentCollective.id);
 		}
@@ -414,16 +419,24 @@
 
 	// ── Suggestions ────────────────────────────────────────────────────────────
 
-	async function updateSuggestions(prefix: string) {
+	// Fase 15: exclude items already in the list so the strip doesn't nudge
+	// the user to re-add what they already have. We snapshot the names here
+	// so the `$effect` below re-fires whenever either the prefix typed or
+	// the list contents change.
+	const excludedItemNames = $derived(items.map((i) => i.name));
+
+	async function updateSuggestions(prefix: string, exclude: string[]) {
 		clearTimeout(suggestionsTimer);
 		if (!$currentCollective) return;
 		suggestionsTimer = setTimeout(async () => {
-			suggestions = await fetchSuggestions($currentCollective!.id, prefix);
+			suggestions = await fetchSuggestions($currentCollective!.id, prefix, {
+				excludeNames: exclude
+			});
 		}, 150);
 	}
 
 	$effect(() => {
-		updateSuggestions(newName);
+		updateSuggestions(newName, excludedItemNames);
 	});
 
 	function selectSuggestion(name: string) {