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/lib/theme/themes/ayu-light.json

@@ -30,7 +30,7 @@
       "subtle": "#FFF7E5"
     },
     "interactive": {
-      "border": "#E6DDCF",
+      "border": "#ece5d9",
       "borderHover": "#DCD3C5",
       "borderFocus": "#B09F8F",
       "selection": "#9fb2c43e",