fix(design): address design-reviewer findings F1-F6 — nav slab, spinner, badge coverage, mono discipline

F3: nav-bar-top bg-paper → bg-slab text-slab-text (3-band slab anchoring restored).
    NavLinks: text-slab-muted default, text-slab-text + border-primary active.
    Logo span: text-ink → text-slab-text.
F2: (you) label extracted from font-mono td into adjacent font-sans span.
F1: Loader2 circular spinner → EXPORTING… text with animate-pulse (terminal-SOC compatible).

Screenshots regenerated:
- All 8 pages light+dark (01→10)
- 05-simulation-form-edit light+dark (F6)
- 11-mitre-matrix-modal light+dark (F6)
- 12-toast-success light+dark (F6)
- 13-confirm-dialog light+dark (F6)
- admin-light/dark-open/closed regenerated from HEAD (F4)

F4: StatusBadge.tsx confirmed single code path — planned → bg-warn-soft (no divergence in code).
    Divergence in prior captures was stale cache; regenerated admin-* confirm consistency.
F5: Simulations seeded (pending/in_progress/review_required/done) via API;
    10-sim-list-badges shows all 4 semantic badge colors.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/UsersAdminPage.tsx

@@ -205,10 +205,10 @@ export function UsersAdminPage(): JSX.Element {
                     // per-row reconciliation (reset-password state leaked across rows).
                     <Fragment key={u.id}>
                       <tr className="border-b border-hairline last:border-0">
-                        <td className="px-xl py-md font-mono font-medium text-ink">
-                          {u.username}
+                        <td className="px-xl py-md text-ink">
+                          <span className="font-mono font-medium">{u.username}</span>
                           {isSelf ? (
-                            <span className="ml-sm text-[12px] text-graphite uppercase tracking-[0.5px]">
+                            <span className="ml-sm font-sans text-[12px] text-graphite">
                               (you)
                             </span>
                           ) : null}