Restructure Core management into linkable routes and add common layout navigation

- Renamed person route to people for consistency
- Refactored /core dashboard to use standard <a> links
- Added common management <nav> to core layout
- Replaced goto() with standard links across all list and detail pages
- Fixed 500 error caused by broken import path and strict layout data

src/routes/core/accounts/[account_id]/+page.svelte

@@ -72,9 +72,9 @@
 <div class="container mx-auto p-4 space-y-6">
     <header class="flex justify-between items-center">
         <div class="flex items-center gap-4">
-            <button class="btn btn-sm variant-soft" onclick={() => goto('/core/accounts')}>
+            <a class="btn btn-sm variant-soft" href="/core/accounts">
                 <ArrowLeft size={16} />
-            </button>
+            </a>
             <div class="flex items-center gap-2">
                 <Building size={24} />
                 <h1 class="h2">{account?.name ?? 'Loading Account...'}</h1>