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/blossom.go

@@ -20,8 +20,12 @@ func initializeBlossomServer(
 	blossomCfg := &blossom.Config{
 		BaseURL:          "", // Will be set dynamically per request
 		MaxBlobSize:      100 * 1024 * 1024, // 100MB default
-		AllowedMimeTypes: nil,                // Allow all MIME types by default
+		AllowedMimeTypes: nil,               // Allow all MIME types by default
 		RequireAuth:      cfg.AuthRequired || cfg.AuthToWrite,
+		// Rate limiting for non-followed users
+		RateLimitEnabled: cfg.BlossomRateLimitEnabled,
+		DailyLimitMB:     cfg.BlossomDailyLimitMB,
+		BurstLimitMB:     cfg.BlossomBurstLimitMB,
 	}
 
 	// Create blossom server with relay's ACL registry
@@ -31,7 +35,12 @@ func initializeBlossomServer(
 	// We'll need to modify the handler to inject the baseURL per request
 	// For now, we'll use a middleware approach
 
-	log.I.F("blossom server initialized with ACL mode: %s", cfg.ACLMode)
+	if cfg.BlossomRateLimitEnabled {
+		log.I.F("blossom server initialized with ACL mode: %s, rate limit: %dMB/day (burst: %dMB)",
+			cfg.ACLMode, cfg.BlossomDailyLimitMB, cfg.BlossomBurstLimitMB)
+	} else {
+		log.I.F("blossom server initialized with ACL mode: %s", cfg.ACLMode)
+	}
 	return bs, nil
 }