fix: answer the round-33 nits on the hub route and the empty state

- `empty_state_view` is no longer logged for an archived-only workspace, which
  is not the state the counter measures.
- `detail`'s fetcher keeps its last answer in a local instead of reading
  `detail.current`, a self-reference that typed the resource `any`.
- `list_projects`' comment, including its authorization contract, is back on the
  handler rather than on the predicate inserted above it.
- `listHubProjects` documents the 400 an instance with the hub disabled returns.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012fRjnaHLwjpHN84gNNxah9

frontend/src/lib/components/home/ImportProjectModal.svelte

@@ -145,12 +145,16 @@
 	// previous controller but `fetchHubProject` takes no signal, and nothing orders the
 	// responses — so picking A, dismissing, then picking B can land A's name, author and
 	// counts over an import that writes B.
+	// Kept in a local rather than read back off `detail.current` inside `detail`'s own fetcher,
+	// which makes the resource's type circular and resolves it to `any`.
+	let lastDetail = $state<ImportProjectSummary | undefined>(undefined)
 	const detail = resource(
 		() => slug,
 		async (s) => {
 			if (!s) return undefined
 			const fetched = await fetchHubProject(s)
-			return s === slug ? fetched : detail.current
+			if (s === slug) lastDetail = fetched
+			return lastDetail
 		}
 	)
 	let project = $derived<ImportProjectSummary | undefined>(

frontend/src/lib/components/home/WorkspaceEmptyState.svelte

@@ -40,7 +40,9 @@
 	let newLinkEl: HTMLButtonElement | undefined = $state(undefined)
 
 	onMount(() => {
-		logFeatureUsage('home', 'empty_state_view')
+		// Only the empty case: the counter answers how many workspaces sit empty and what
+		// their owners do next, and a workspace whose items are all archived is neither.
+		if (!archivedOnly) logFeatureUsage('home', 'empty_state_view')
 	})
 
 	// The catalogue is fetched when the picker opens, never on render: `disable_hub` says an