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/styles/design-system.css

@@ -101,15 +101,7 @@
   }
 
   * {
-    border-color: hsl(var(--border));
-  }
-
-  :root * {
-    border-color: rgba(194, 151, 77, 0.2); /* Warm golden sand borders for light mode */
-  }
-
-  .dark * {
-    border-color: rgba(57, 56, 54, 0.5); /* #393836 at 50% opacity */
+    border-color: var(--border); /* Theme border token (interactive.border) — opaque and theme-aware */
   }
 
   body {