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

2 files changed, 24 insertions, 2 deletions

diff --git a/internal/server/server.go b/internal/server/server.go
index 8681873..6d76fa0 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -17,6 +17,7 @@ import (
 	"github.com/Fuwn/kaze/internal/config"
 	"github.com/Fuwn/kaze/internal/monitor"
 	"github.com/Fuwn/kaze/internal/storage"
+	"github.com/Fuwn/kaze/internal/theme"
 )
 
 //go:embed templates/*.html
@@ -126,8 +127,9 @@ type PageData struct {
 	TickMode           string // ping, minute, hour, day
 	TickCount          int
 	ShowThemeToggle    bool
-	Timezone           string // Timezone for display
-	UseBrowserTimezone bool   // Use client-side timezone conversion
+	Timezone           string       // Timezone for display
+	UseBrowserTimezone bool         // Use client-side timezone conversion
+	ThemeCSS           template.CSS // OpenCode theme CSS (safe CSS)
 }
 
 // GroupData contains data for a monitor group
@@ -190,6 +192,19 @@ func (s *Server) handleIndex(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Load OpenCode theme if configured
+	var themeCSS template.CSS
+	if s.config.Site.ThemeURL != "" {
+		resolvedTheme, err := theme.LoadTheme(s.config.Site.ThemeURL)
+		if err != nil {
+			s.logger.Warn("failed to load theme", "url", s.config.Site.ThemeURL, "error", err)
+		} else if resolvedTheme != nil {
+			// Generate CSS variables and Tailwind mappings
+			cssString := resolvedTheme.GenerateCSS() + resolvedTheme.GenerateTailwindMappings()
+			themeCSS = template.CSS(cssString)
+		}
+	}
+
 	// Build page data
 	data := PageData{
 		Site:               s.config.Site,
@@ -198,6 +213,7 @@ func (s *Server) handleIndex(w http.ResponseWriter, r *http.Request) {
 		ShowThemeToggle:    s.config.Display.ShowThemeToggle != nil && *s.config.Display.ShowThemeToggle,
 		Timezone:           s.config.Display.Timezone,
 		UseBrowserTimezone: s.config.Display.Timezone == "Browser",
+		ThemeCSS:           themeCSS,
 	}
 
 	overallUp := true
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)) {