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/jetbrains-light.json

@@ -30,10 +30,10 @@
       "elevated": "#FFFFFF",
       "elevatedForeground": "#000000",
       "overlay": "#00000025",
-      "subtle": "#ecf0f8"
+      "subtle": "#f5f8fd"
     },
     "interactive": {
-      "border": "#cfd3de",
+      "border": "#dde0ea",
       "borderHover": "#AEB3C2",
       "borderFocus": "#0055FF",
       "selection": "#DFE1E5",
@@ -145,7 +145,7 @@
     },
     "chat": {
       "userMessage": "#000000",
-      "userMessageBackground": "#E8F1FF",
+      "userMessageBackground": "#eff4fd",
       "assistantMessage": "#000000",
       "assistantMessageBackground": "#F7F8FA",
       "timestamp": "#767A8A",