feat: Add SVG status badge endpoint

GET /api/badge/{name}.svg - Shields.io style status badges (always public)

Options:
- ?label=Custom    - Override the label text (default: monitor name)
- ?style=flat|plastic - Badge style (default: flat)
- ?type=status|uptime - Show status or uptime percentage (default: status)

Colors:
- Green (#22c55e) for up / >=99% uptime
- Yellow (#eab308) for degraded / >=95% uptime
- Red (#ef4444) for down / <95% uptime
- Gray (#9ca3af) for unknown

Example: ![Status](https://status.example.com/api/badge/Website.svg)

2 files changed, 134 insertions, 0 deletions

diff --git a/config.example.yaml b/config.example.yaml
index 706e3dc..91d17e9 100644
--- a/config.example.yaml
+++ b/config.example.yaml
@@ -379,6 +379,9 @@ incidents:
 #                                  Supports ?period=1h|24h|7d|30d|90d (default: 24h)
 #     GET /api/incidents         - List incidents from config
 #                                  Supports ?filter=all|active|resolved|scheduled (default: all)
+#     GET /api/badge/{name}.svg  - SVG status badge (always public, shields.io style)
+#                                  Supports: ?label=custom&style=flat|plastic&type=status|uptime
+#                                  Example: ![Status](https://status.example.com/api/badge/Website.svg)
 #   
 #   Authentication (when access is "authenticated"):
 #     - Header: X-API-Key: your-secret-key
diff --git a/internal/server/server.go b/internal/server/server.go
index 86ee2a3..b835955 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -77,6 +77,9 @@ func New(cfg *config.Config, store *storage.Storage, sched *monitor.Scheduler, l
 	// Health check - always public (for load balancers, monitoring)
 	mux.HandleFunc("GET /api/health", s.handleAPIHealth)
 
+	// Badge endpoint - always public (for embedding in READMEs, docs)
+	mux.HandleFunc("GET /api/badge/{name}.svg", s.handleAPIBadge)
+
 	// Full page data endpoint - public if refresh_mode=api, otherwise follows api.access
 	if cfg.Display.RefreshMode == "api" {
 		mux.HandleFunc("GET /api/page", s.handleAPIPage)
@@ -648,6 +651,134 @@ func (s *Server) handleAPIHealth(w http.ResponseWriter, r *http.Request) {
 	s.jsonResponse(w, map[string]string{"status": "ok"})
 }
 
+// handleAPIBadge returns an SVG status badge for a monitor (shields.io style)
+func (s *Server) handleAPIBadge(w http.ResponseWriter, r *http.Request) {
+	name := r.PathValue("name")
+	if name == "" {
+		http.Error(w, "Monitor name required", http.StatusBadRequest)
+		return
+	}
+
+	// Get monitor stats
+	stats, err := s.storage.GetMonitorStats(r.Context(), name)
+	if err != nil {
+		s.logger.Error("failed to get monitor stats for badge", "monitor", name, "error", err)
+		// Return a gray "unknown" badge on error
+		s.serveBadge(w, r, name, "unknown", "#9ca3af")
+		return
+	}
+
+	// Determine status and color
+	var status, color string
+	switch stats.CurrentStatus {
+	case "up":
+		status = "up"
+		color = "#22c55e" // green-500
+	case "degraded":
+		status = "degraded"
+		color = "#eab308" // yellow-500
+	case "down":
+		status = "down"
+		color = "#ef4444" // red-500
+	default:
+		status = "unknown"
+		color = "#9ca3af" // gray-400
+	}
+
+	// Check for custom label
+	label := r.URL.Query().Get("label")
+	if label == "" {
+		label = name
+	}
+
+	// Check for style (flat or plastic, default: flat)
+	style := r.URL.Query().Get("style")
+	if style != "plastic" {
+		style = "flat"
+	}
+
+	// Check if uptime should be shown instead of status
+	if r.URL.Query().Get("type") == "uptime" {
+		status = fmt.Sprintf("%.1f%%", stats.UptimePercent)
+		if stats.UptimePercent >= 99.0 {
+			color = "#22c55e"
+		} else if stats.UptimePercent >= 95.0 {
+			color = "#eab308"
+		} else {
+			color = "#ef4444"
+		}
+	}
+
+	s.serveBadge(w, r, label, status, color)
+}
+
+// serveBadge generates and serves an SVG badge
+func (s *Server) serveBadge(w http.ResponseWriter, r *http.Request, label, status, color string) {
+	style := r.URL.Query().Get("style")
+	if style != "plastic" {
+		style = "flat"
+	}
+
+	// Calculate widths (approximate, 6px per character + padding)
+	labelWidth := len(label)*6 + 10
+	statusWidth := len(status)*6 + 10
+	totalWidth := labelWidth + statusWidth
+
+	var svg string
+	if style == "plastic" {
+		// Plastic style with gradient
+		svg = fmt.Sprintf(`<svg xmlns="http://www.w3.org/2000/svg" width="%d" height="20">
+  <linearGradient id="b" x2="0" y2="100%%">
+    <stop offset="0" stop-color="#fff" stop-opacity=".7"/>
+    <stop offset=".1" stop-color="#aaa" stop-opacity=".1"/>
+    <stop offset=".9" stop-color="#000" stop-opacity=".3"/>
+    <stop offset="1" stop-color="#000" stop-opacity=".5"/>
+  </linearGradient>
+  <clipPath id="a">
+    <rect width="%d" height="20" rx="3" fill="#fff"/>
+  </clipPath>
+  <g clip-path="url(#a)">
+    <rect width="%d" height="20" fill="#555"/>
+    <rect x="%d" width="%d" height="20" fill="%s"/>
+    <rect width="%d" height="20" fill="url(#b)"/>
+  </g>
+  <g fill="#fff" text-anchor="middle" font-family="DejaVu Sans,Verdana,Geneva,sans-serif" font-size="11">
+    <text x="%d" y="15" fill="#010101" fill-opacity=".3">%s</text>
+    <text x="%d" y="14">%s</text>
+    <text x="%d" y="15" fill="#010101" fill-opacity=".3">%s</text>
+    <text x="%d" y="14">%s</text>
+  </g>
+</svg>`,
+			totalWidth, totalWidth, labelWidth, labelWidth, statusWidth, color, totalWidth,
+			labelWidth/2, label, labelWidth/2, label,
+			labelWidth+statusWidth/2, status, labelWidth+statusWidth/2, status)
+	} else {
+		// Flat style (default)
+		svg = fmt.Sprintf(`<svg xmlns="http://www.w3.org/2000/svg" width="%d" height="20">
+  <clipPath id="a">
+    <rect width="%d" height="20" rx="3" fill="#fff"/>
+  </clipPath>
+  <g clip-path="url(#a)">
+    <rect width="%d" height="20" fill="#555"/>
+    <rect x="%d" width="%d" height="20" fill="%s"/>
+  </g>
+  <g fill="#fff" text-anchor="middle" font-family="DejaVu Sans,Verdana,Geneva,sans-serif" font-size="11">
+    <text x="%d" y="15" fill="#010101" fill-opacity=".3">%s</text>
+    <text x="%d" y="14">%s</text>
+    <text x="%d" y="15" fill="#010101" fill-opacity=".3">%s</text>
+    <text x="%d" y="14">%s</text>
+  </g>
+</svg>`,
+			totalWidth, totalWidth, labelWidth, labelWidth, statusWidth, color,
+			labelWidth/2, label, labelWidth/2, label,
+			labelWidth+statusWidth/2, status, labelWidth+statusWidth/2, status)
+	}
+
+	w.Header().Set("Content-Type", "image/svg+xml")
+	w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
+	w.Write([]byte(svg))
+}
+
 // APISummaryResponse contains a lightweight status overview
 type APISummaryResponse struct {
 	OverallStatus string       `json:"overall_status"`