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/StatusPill.tsx

@@ -0,0 +1,48 @@
+import { Laptop, Monitor, Terminal, type LucideIcon } from "lucide-react";
+
+import { cn } from "@/lib/cn";
+import type { SystemStatus } from "@/lib/types";
+
+const osIcons: Record<string, LucideIcon> = {
+  linux: Terminal,
+  apple: Laptop,
+  windows: Monitor,
+};
+
+function formatMs(value: number): string {
+  return value >= 100 ? `${Math.round(value)}ms` : `${value.toFixed(1)}ms`;
+}
+
+export function StatusPill({ status }: { status?: SystemStatus }) {
+  if (!status) return null;
+  const OsIcon = osIcons[status.os.icon] ?? Monitor;
+
+  return (
+    <span
+      className="hidden select-none items-center gap-1.5 rounded-full border border-ctp-surface0 bg-ctp-mantle px-2.5 py-1 font-mono text-[11px] text-ctp-overlay1 lg:flex"
+      title={`${status.os.name} ${status.os.release} · built from ${status.git_hash}`}
+    >
+      <span
+        className={cn(
+          "font-medium",
+          status.env === "prod" ? "text-ctp-teal" : "text-ctp-yellow",
+        )}
+      >
+        ENV: {status.env.toUpperCase()}
+      </span>
+      <span className="text-ctp-surface2">·</span>
+      <span>{status.git_hash}</span>
+      <span className="text-ctp-surface2">·</span>
+      <OsIcon className="h-3 w-3" />
+      <span>{status.os.name.toUpperCase()}</span>
+      <span className="text-ctp-surface2">·</span>
+      <span>{formatMs(status.server_time_ms)}</span>
+      {status.e621_time_ms !== null ? (
+        <>
+          <span className="text-ctp-surface2">·</span>
+          <span>e621: {formatMs(status.e621_time_ms)}</span>
+        </>
+      ) : null}
+    </span>
+  );
+}