fix(types): resolve pre-existing svelte-check errors

stale-containers page referenced container.id but StaleContainer wraps an
inner instance object — switch to container.instance.id at the three call
sites. env editor derived projectId from $page.params.id (string |
undefined); coalesce to empty string so call sites that pass it to API
helpers don't trip the strictNullChecks gate.

Pre-existing errors flagged by `svelte-check`; not introduced by recent
feature work but blocking the green check.

web/src/routes/containers/stale/+page.svelte

@@ -41,7 +41,7 @@
 		cleaningIds = new Set([...cleaningIds, id]);
 		try {
 			await api.cleanupStaleContainer(id);
-			containers = containers.filter((c) => c.id !== id);
+			containers = containers.filter((c) => c.instance.id !== id);
 			toasts.success($t('stale.cleanedUp'));
 		} catch (e) {
 			toasts.error(e instanceof Error ? e.message : $t('stale.cleanupFailed'));
@@ -124,10 +124,10 @@
 		/>
 	{:else}
 		<div class="grid grid-cols-1 gap-4 sm:grid-cols-2 lg:grid-cols-3">
-			{#each containers as container (container.id)}
+			{#each containers as container (container.instance.id)}
 				<StaleContainerCard
 					{container}
-					cleaning={cleaningIds.has(container.id)}
+					cleaning={cleaningIds.has(container.instance.id)}
 					oncleanup={requestCleanup}
 				/>
 			{/each}

web/src/routes/projects/[id]/env/+page.svelte

@@ -40,7 +40,10 @@
 	let editProjectValue = $state('');
 	let projectEnvDeleteTarget = $state<string | null>(null);
 
-	const projectId = $derived($page.params.id);
+	// $page.params.id is typed string | undefined because SvelteKit can't
+	// statically prove the [id] segment is present, but inside this route file
+	// it always is — assert non-null so call sites don't need their own guards.
+	const projectId = $derived($page.params.id ?? '');
 
 	async function handleAddProjectEnv() {
 		if (!newProjectKey.trim()) return;