feat: Add OpenCode-compatible theme loader

Add support for loading and applying OpenCode-compatible themes via URL.
Fetches theme JSON, resolves color references, generates CSS variables
and Tailwind class overrides to apply the theme seamlessly.

Features:
- Add theme_url config field under site section
- Fetch and parse OpenCode theme.json format
- Generate CSS custom properties (--theme-*) for all theme colors
- Generate Tailwind class overrides to apply theme colors
- Support both light and dark modes
- Template.CSS type for safe CSS injection

Example usage:
  site:
    theme_url: "https://raw.githubusercontent.com/anomalyco/opencode/.../opencode.json"

Theme schema: https://opencode.ai/theme.json

1 files changed, 6 insertions, 0 deletions

diff --git a/internal/server/templates/index.html b/internal/server/templates/index.html
index db4c61a..6bdfeff 100644
--- a/internal/server/templates/index.html
+++ b/internal/server/templates/index.html
@@ -11,6 +11,12 @@
     <link rel="icon" href="data:image/svg+xml,<svg xmlns=%22http://www.w3.org/2000/svg%22 viewBox=%220 0 100 100%22><text y=%22.9em%22 font-size=%2290%22>🎐</text></svg>">
     {{end}}
     <link rel="stylesheet" href="/static/style.css">
+    {{if .ThemeCSS}}
+    <style>
+        /* OpenCode Theme */
+{{.ThemeCSS}}
+    </style>
+    {{end}}
     <script>
         // Theme detection
         if (localStorage.theme === 'dark' || (!('theme' in localStorage) && window.matchMedia('(prefers-color-scheme: dark)').matches)) {