Shell polish: storage line, status pill, footer strip, sidebar

Backend:
- apps.core with GET /api/status/ (env, git hash, OS, watched folder,
  worker counts) and a TimingMiddleware adding X-Server-Time-Ms
- status endpoint reports its own server-side assembly time

Frontend:
- top bar shows the storage line (watched folder) and a status pill
  with ENV, git hash, host OS, server time (e621 time once it exists)
- fixed 32px footer strip: storage path, active workers, build version
- collapsible filter sidebar: closed by default, Ctrl/Cmd+B toggle,
  overlay drawer with backdrop blur under 1024px
- rating filters, per-page and sidebar state persist in localStorage

frontend/src/components/StatusFooter.tsx

@@ -0,0 +1,38 @@
+import { Folder, Zap } from "lucide-react";
+
+import type { SystemStatus } from "@/lib/types";
+import { APP_VERSION } from "@/lib/version";
+
+export function StatusFooter({ status }: { status?: SystemStatus }) {
+  return (
+    <footer className="fixed inset-x-0 bottom-0 z-30 border-t border-ctp-surface0 bg-ctp-crust">
+      <div className="mx-auto flex h-8 w-full max-w-[1600px] items-center gap-4 px-4 font-mono text-[11px] text-ctp-overlay0">
+        <span
+          className="flex min-w-0 items-center gap-1.5"
+          title={status?.watched_folder ?? ""}
+        >
+          <Folder className="h-3 w-3 shrink-0" />
+          <span className="hidden shrink-0 sm:inline">Local Storage:</span>
+          <span className="truncate">{status?.watched_folder ?? "…"}</span>
+        </span>
+
+        <span
+          className="hidden shrink-0 items-center gap-1.5 md:flex"
+          title="Active background jobs"
+        >
+          <Zap className="h-3 w-3" />
+          <span>
+            Active Workers:{" "}
+            {status
+              ? `${status.workers.active} running | ${status.workers.queued} pending`
+              : "…"}
+          </span>
+        </span>
+
+        <span className="ml-auto shrink-0" title="Running build">
+          {status?.version ?? APP_VERSION}
+        </span>
+      </div>
+    </footer>
+  );
+}