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/dracula-dark.json

@@ -27,10 +27,10 @@
       "elevated": "#161722",
       "elevatedForeground": "#F8F8F2",
       "overlay": "#FFFFFF20",
-      "subtle": "#222436"
+      "subtle": "#1f2030"
     },
     "interactive": {
-      "border": "#2D2F3C",
+      "border": "#292a36",
       "borderHover": "#303244",
       "borderFocus": "#4A4D6D",
       "selection": "#30334b",