refactor: full codebase overhaul — dead code removal, env validation, logger migration, date consolidation, Prisma schema cleanup, button consistency, useEffect deps, test coverage

- env.ts: added 10 missing Zod-validated env vars (imager, paypal currency, argon2/bcrypt params)
- Migrated 6 modules from process.env to validated env.* (auth, proxy-auth, paypal, password, redis, imager, moderation, alert, logger)
- Replaced console.warn/error with pino logger in 9 server-side modules
- Removed 50+ dead exports (SWF wrappers, coalesceHotelName, signIn, isStaff re-export, formatTimestamp, Skeleton/SkeletonCard, 4 unused housekeeping sections)
- Consolidated date formatting: 28 files migrated to shared formatDate() from @/lib/format-date
- Wired 4 radio/settings API routes through cached siteSettings service instead of raw Prisma queries
- Added getMany()/getAll() helpers to SiteSettings service
- Removed 88 dead Prisma model definitions (schema 2763→1846 lines)
- Created admin action-helper.ts with wrapAction() for standardized error handling
- Fixed useEffect dependency arrays in 4 data-heavy components
- Replaced raw btn CSS classes with shadcn Button component across admin pages
- Stripped dead i18n namespaces (common, pages.client) from all 22 translation files
- Removed 2 dead scripts (create-release.sh, check-local-imports.ts)
- Fixed knip.json configuration
- Added 7 new test suites: format-date, paypal, moderation, alert, webhook, action-helper, and fixed password.test.ts for env mocking
- All 358 tests passing across 72 test files
- TypeScript: 0 errors

src/app/admin/error.tsx

@@ -5,6 +5,7 @@ import { LayoutDashboard, RefreshCw } from "lucide-react";
 import Link from "next/link";
 import { useTranslations } from "next-intl";
 import { useEffect } from "react";
+import { Button } from "@/components/ui/button";
 
 /**
  * Admin route-segment error boundary. Renders inside the admin layout shell.
@@ -47,14 +48,16 @@ export default function AdminErrorPage({
 				{t("body")}
 			</p>
 			<div className="flex flex-wrap gap-3 justify-center">
-				<button type="button" className="btn btn-primary" onClick={() => reset()}>
+				<Button type="button" variant="default" onClick={() => reset()}>
 					<RefreshCw className="size-4" aria-hidden />
 					{t("tryAgain")}
-				</button>
-				<Link className="btn btn-outline" href="/admin">
-					<LayoutDashboard className="size-4" aria-hidden />
-					{tNav("dashboard")}
-				</Link>
+				</Button>
+				<Button variant="outline" asChild>
+					<Link href="/admin">
+						<LayoutDashboard className="size-4" aria-hidden />
+						{tNav("dashboard")}
+					</Link>
+				</Button>
 			</div>
 			{error.digest ? (
 				<p