feat(admin): add orange rgb(241,119,50) as an exact brand-color option

Revert the earlier mis-scoped orange on the personalization panel and
instead expose rgb(241,119,50) as a selectable 'رنگ اصلی' swatch. When
picked it overrides --primary/-600/-700/-soft/-soft2/-ring inline with
exact hex, so every var(--primary) consumer across the whole admin
(buttons, active nav, rings) becomes that orange. Non-fixed hues keep
the oklch hue pipeline (inline overrides removed on switch).

- uiStore: BrandHue interface + optional fixed hex; shared applyBrand()
  helper handles fixed vs hue, dark-aware soft tints
- AdminLayout: reuse applyBrand() (no divergence with store)
- Topbar: swatch shows the exact fixed color
- tests: fixed-color apply, dark soft, and override-cleanup on switch

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

assets/admin/styles.css

@@ -658,9 +658,6 @@ table.t tbody tr:last-child td { border-bottom: none; }
   animation: slidein .3s var(--ease);
   border-radius: 0; max-height: 100%;
 }
-/* رنگ اختصاصی بخش «شخصی‌سازی» — فقط همین پنل، نه جای دیگر پنل */
-.settings-panel .modal-head h2 { color: rgb(241, 119, 50); }
-.settings-panel .seg button.on { background: rgb(241, 119, 50); color: #fff; box-shadow: var(--shadow-sm); }
 
 /* ── Form rows ───────────────────────────────────────────────── */
 .form-row { display: flex; flex-direction: column; gap: 7px; margin-bottom: 16px; }