Add progressive throttle for follows ACL mode (v0.48.10)

- Add progressive throttle feature for follows ACL mode, allowing
  non-followed users to write with increasing delay instead of blocking
- Delay increases linearly per event (default 200ms) and decays at 1:1
  ratio with elapsed time, capping at configurable max (default 60s)
- Track both IP and pubkey independently to prevent evasion
- Add periodic cleanup to remove fully-decayed throttle entries
- Fix BBolt serial resolver to return proper errors when buckets or
  entries are not found

Files modified:
- app/config/config.go: Add ORLY_FOLLOWS_THROTTLE_* env vars
- app/handle-event.go: Apply throttle delay before event processing
- app/listener.go: Add getFollowsThrottleDelay helper method
- pkg/acl/follows.go: Integrate throttle with follows ACL
- pkg/acl/follows_throttle.go: New progressive throttle implementation
- pkg/bbolt/save-event.go: Return errors from serial lookups
- pkg/version/version: Bump to v0.48.10

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/config/config.go

@@ -67,6 +67,11 @@ type C struct {
 	ClusterAdmins       []string      `env:"ORLY_CLUSTER_ADMINS" usage:"comma-separated list of npubs authorized to manage cluster membership"`
 	FollowListFrequency time.Duration `env:"ORLY_FOLLOW_LIST_FREQUENCY" usage:"how often to fetch admin follow lists (default: 1h)" default:"1h"`
 
+	// Progressive throttle for follows ACL mode - allows non-followed users to write with increasing delay
+	FollowsThrottleEnabled  bool          `env:"ORLY_FOLLOWS_THROTTLE" default:"false" usage:"enable progressive delay for non-followed users in follows ACL mode"`
+	FollowsThrottlePerEvent time.Duration `env:"ORLY_FOLLOWS_THROTTLE_INCREMENT" default:"200ms" usage:"delay added per event for non-followed users"`
+	FollowsThrottleMaxDelay time.Duration `env:"ORLY_FOLLOWS_THROTTLE_MAX" default:"60s" usage:"maximum throttle delay cap"`
+
 	// Blossom blob storage service level settings
 	BlossomServiceLevels string `env:"ORLY_BLOSSOM_SERVICE_LEVELS" usage:"comma-separated list of service levels in format: name:storage_mb_per_sat_per_month (e.g., basic:1,premium:10)"`
 
@@ -841,3 +846,15 @@ func (cfg *C) GetNRCConfigValues() (
 		cfg.NRCUseCashu,
 		sessionTimeout
 }
+
+// GetFollowsThrottleConfigValues returns the progressive throttle configuration values
+// for the follows ACL mode. This allows non-followed users to write with increasing delay.
+func (cfg *C) GetFollowsThrottleConfigValues() (
+	enabled bool,
+	perEvent time.Duration,
+	maxDelay time.Duration,
+) {
+	return cfg.FollowsThrottleEnabled,
+		cfg.FollowsThrottlePerEvent,
+		cfg.FollowsThrottleMaxDelay
+}