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>

pkg/acl/follows.go

@@ -138,7 +138,7 @@ func (f *Follows) Configure(cfg ...any) (err error) {
 	if f.cfg.FollowsThrottleEnabled {
 		perEvent := f.cfg.FollowsThrottlePerEvent
 		if perEvent == 0 {
-			perEvent = 200 * time.Millisecond
+			perEvent = 25 * time.Millisecond
 		}
 		maxDelay := f.cfg.FollowsThrottleMaxDelay
 		if maxDelay == 0 {