phase-6: typescript introduction

ui/src/routes/safe-buys/+page.svelte

@@ -1,10 +1,17 @@
-<script>
+<script lang="ts">
   import MarketContext from '$lib/MarketContext.svelte';
   import SignalBadge from '$lib/SignalBadge.svelte';
   import VerdictPill from '$lib/VerdictPill.svelte';
   import { sorted } from '$lib/utils.js';
+  import type { AssetResult, MarketContext as MarketContextType } from '$lib/types.js';
 
-  let { data } = $props();
+  interface PageData {
+    ETF:           AssetResult[];
+    BOND:          AssetResult[];
+    marketContext: MarketContextType | null;
+    error?:        string;
+  }
+  let { data }: { data: PageData } = $props();
 
   const SIGNAL_STRONG = '✅ Strong Buy';