feat(mvp): phase 8 - integration, testing & deployment

Fix all build/type/lint errors (zod 3.25 compat wrapper, Svelte 5 fixes),
write 115 unit tests across 10 test files, expand seed script with demo
data, update Docker config with migration on startup.

src/routes/admin/+layout.svelte

@@ -22,7 +22,7 @@
 		<div class="mb-6 flex flex-wrap items-center gap-4 rounded-xl border border-border bg-card p-4 shadow-sm">
 			<span class="text-sm font-semibold text-foreground">Admin Panel</span>
 			<div class="flex gap-1">
-				{#each navItems as item}
+				{#each navItems as item (item.href)}
 					<a
 						href={item.href}
 						class="rounded-lg px-3 py-1.5 text-sm font-medium transition-colors {isActive(item.href)