Phase 7: polish — overview health, reduced-motion, mobile, a11y, copy-ids

- Overview health hero derives from subsystem probes when the backend gives no
  overall status, so it never says "Unknown" next to an all-Healthy Subsystems
  card (the audit's most jarring contradiction). Home error copy now uses the
  Phase-2 describeError instead of raw backend strings.
- Global prefers-reduced-motion guard (transitions, loops, aurora field) +
  motion-reduce on the sidebar width transition.
- Mobile: content reserves a top row (pt-16 md:p-6) so the floating hamburger
  never overlaps the page H1.
- A11y: collapsed rail items get an explicit aria-label.
- Monitoring: disk "busiest mount" tile shows the % as the value and the long
  mount path as a truncated caption, so it no longer clips mid-word.
- New CopyId component (click-to-copy UUIDs), wired into Profile.

Typecheck 36→36, 24-route sweep clean. Remaining items (lib a11y labels,
table aria-sort, dev-only monitoring data) noted in the spec.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/components/copy-id.tsx

@@ -0,0 +1,51 @@
+import { useState } from "react"
+import { Check, Copy } from "lucide-react"
+
+/**
+ * A monospace id (UUID, slug, token name) that copies to the clipboard on
+ * click, with a brief checkmark. Raw ids are common in an admin console and
+ * useless if you can't get them into a support ticket or a CLI.
+ */
+export function CopyId({
+  value,
+  label,
+  className = "",
+  dataAction,
+}: {
+  value: string
+  /** What's being copied, for the aria-label. Defaults to "id". */
+  label?: string
+  className?: string
+  dataAction?: string
+}) {
+  const [copied, setCopied] = useState(false)
+
+  const copy = async () => {
+    try {
+      await navigator.clipboard.writeText(value)
+      setCopied(true)
+      setTimeout(() => setCopied(false), 1200)
+    } catch {
+      // Clipboard blocked (insecure context / permissions) — no-op; the value
+      // is still selectable by hand.
+    }
+  }
+
+  return (
+    <button
+      type="button"
+      onClick={copy}
+      data-action={dataAction}
+      aria-label={`Copy ${label ?? "id"}`}
+      title="Copy"
+      className={`group inline-flex max-w-full items-center gap-1 rounded bg-muted px-1.5 py-0.5 font-mono text-xs transition-colors hover:bg-accent ${className}`}
+    >
+      <span className="truncate">{value}</span>
+      {copied ? (
+        <Check className="size-3 shrink-0 text-emerald-500" />
+      ) : (
+        <Copy className="size-3 shrink-0 text-muted-foreground opacity-0 transition-opacity group-hover:opacity-100" />
+      )}
+    </button>
+  )
+}