Add dynamic OG image generation for rich iMessage/social previews

Generates a branded 1200x630 PNG per event with title, date/time/location
using Go's image package and a custom bitmap font. Supports BBQ_BASE_URL
env var for absolute URLs required by link preview crawlers.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

main.go

@@ -32,18 +32,20 @@ var schemaSQL string
 var pageTmpl map[string]*template.Template
 
 type Server struct {
-	q  *db.Queries
-	db *sql.DB
+	q       *db.Queries
+	db      *sql.DB
+	baseURL string
 
 	// SSE: map of event slug -> set of channels
 	mu      sync.Mutex
 	clients map[string]map[chan struct{}]struct{}
 }
 
-func NewServer(database *sql.DB) *Server {
+func NewServer(database *sql.DB, baseURL string) *Server {
 	return &Server{
 		q:       db.New(database),
 		db:      database,
+		baseURL: baseURL,
 		clients: make(map[string]map[chan struct{}]struct{}),
 	}
 }
@@ -90,6 +92,7 @@ func main() {
 	if v := os.Getenv("PORT"); v != "" {
 		port = v
 	}
+	baseURL := os.Getenv("BBQ_BASE_URL") // e.g. https://bbq.torrtle.co
 
 	database, err := sql.Open("sqlite3", dbPath+"?_journal_mode=WAL&_foreign_keys=on")
 	if err != nil {
@@ -128,7 +131,7 @@ func main() {
 		template.New("").Funcs(funcMap).ParseFS(templateFS, "templates/slots.html"),
 	)
 
-	srv := NewServer(database)
+	srv := NewServer(database, baseURL)
 
 	r := chi.NewRouter()
 	r.Use(middleware.Logger)
@@ -149,6 +152,9 @@ func main() {
 	r.Post("/e/{slug}/rsvp", srv.handleRsvp)
 	r.Delete("/e/{slug}/rsvp/{rsvpID}", srv.handleUnrsvp)
 
+	// OG image
+	r.Get("/e/{slug}/og.png", srv.handleOGImage)
+
 	// SSE
 	r.Get("/e/{slug}/sse", srv.handleSSE)