feat(theme): add OpenChamber hybrid theme and make it the default

- Add OpenChamber brand theme (dark+light): Vitesse syntax over OpenCode-deep neutrals with Flexoki accents, harmonized in OKLCH

- Add scripts/harmonize-theme.mjs: align accent saturation/lightness and boost syntax chroma via OKLCH

- Set default theme to OpenChamber (was Flexoki)

- Rename fields-of-the-shire off the openchamber-* id; keep it as a normal preset

- Remove OpenCode and OC-2 ports and all disabled theme JSON definitions

- Make panel/header/sidebar borders opaque and theme-driven; global default border now uses --border instead of hardcoded rgba

packages/ui/src/components/layout/Sidebar.tsx

@@ -126,7 +126,7 @@ export const Sidebar: React.FC<SidebarProps> = ({ isOpen, isMobile, children, cl
         <aside
             ref={sidebarRef}
             className={cn(
-                'relative flex h-full overflow-hidden border-r border-border/40 will-change-[width] motion-reduce:transition-none',
+                'relative flex h-full overflow-hidden border-r border-border will-change-[width] motion-reduce:transition-none',
                 'bg-sidebar oc-vibrancy-surface',
                 isOpen && 'shadow-[inset_-2px_0_10px_-2px_rgb(0_0_0_/_0.06)]',
                 !isOpen && 'border-r-0',