Add Blossom bandwidth limiting and tune rate limiters (v0.49.0)

- Add token-bucket bandwidth rate limiting for Blossom uploads
  - ORLY_BLOSSOM_RATE_LIMIT enables limiting (default: false)
  - ORLY_BLOSSOM_DAILY_LIMIT_MB sets daily limit (default: 10MB)
  - ORLY_BLOSSOM_BURST_LIMIT_MB sets burst cap (default: 50MB)
  - Followed users, admins, owners are exempt (unlimited)
- Change emergency mode throttling from exponential to linear scaling
  - Old: 16x multiplier at emergency threshold entry
  - New: 1x at threshold, +1x per 20% excess pressure
- Reduce follows ACL throttle increment from 200ms to 25ms per event
- Update dependencies

Files modified:
- app/blossom.go: Pass rate limit config to blossom server
- app/config/config.go: Add Blossom rate limit config options
- pkg/blossom/ratelimit.go: New bandwidth limiter implementation
- pkg/blossom/server.go: Add rate limiter integration
- pkg/blossom/handlers.go: Check rate limits on upload/mirror/media
- pkg/ratelimit/limiter.go: Linear emergency throttling
- pkg/acl/follows.go: Reduce default throttle increment

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/handle-cashu.go

@@ -124,6 +124,17 @@ func (s *Server) handleCashuKeysets(w http.ResponseWriter, r *http.Request) {
 
 // handleCashuInfo handles GET /cashu/info - returns mint information.
 func (s *Server) handleCashuInfo(w http.ResponseWriter, r *http.Request) {
+	// CORS headers for browser-based CAT support detection
+	w.Header().Set("Access-Control-Allow-Origin", "*")
+	w.Header().Set("Access-Control-Allow-Methods", "GET, OPTIONS")
+	w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Accept")
+
+	// Handle preflight
+	if r.Method == http.MethodOptions {
+		w.WriteHeader(http.StatusNoContent)
+		return
+	}
+
 	if s.CashuIssuer == nil {
 		http.Error(w, "Cashu tokens not enabled", http.StatusNotImplemented)
 		return