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/layout/app-shell.tsx

@@ -360,7 +360,7 @@ export function AppShell({
         data-slot="sidebar"
         data-expanded={expanded ? "true" : "false"}
         className={[
-          "sticky top-0 z-30 hidden h-svh shrink-0 flex-col border-r bg-sidebar transition-[width] duration-base ease-standard md:flex",
+          "sticky top-0 z-30 hidden h-svh shrink-0 flex-col border-r bg-sidebar transition-[width] duration-base ease-standard motion-reduce:transition-none md:flex",
           expanded ? "w-60" : "w-16",
         ].join(" ")}
       >
@@ -656,7 +656,10 @@ export function AppShell({
               one floating card in a sea of black. The floating actions
               pill is fixed to the viewport edge and lives outside this
               column, so it stays clear regardless of cap width. */}
-          <div className="mx-auto flex w-full max-w-[1180px] flex-1 flex-col gap-6 p-6 [&>*:first-child]:lg:pr-72">
+          {/* pt-16 on mobile reserves a row for the floating hamburger (left)
+              and actions pill (right) so they never overlap the page H1; the
+              desktop rail/pill sit outside this column, so pt drops to p-6. */}
+          <div className="mx-auto flex w-full max-w-[1180px] flex-1 flex-col gap-6 px-4 pb-6 pt-16 md:p-6 [&>*:first-child]:lg:pr-72">
             <RouteGuard>{children}</RouteGuard>
           </div>
         </div>
@@ -693,6 +696,9 @@ function NavRow({
       to={item.to}
       end={item.end}
       title={expanded ? undefined : item.label}
+      // When collapsed there's no visible label text, only an icon — give
+      // screen readers the name explicitly (title alone isn't reliably read).
+      aria-label={expanded ? undefined : item.label}
       onClick={onNavigate}
       data-action={`${prefix}${item.label.toLowerCase()}`}
       className={({ isActive }) =>