feat: Implement CHORUS scaling improvements for robust autoscaling

Address WHOOSH issue #7 with comprehensive scaling optimizations to prevent
license server, bootstrap peer, and control plane collapse during fast scale-out.

HIGH-RISK FIXES (Must-Do):
✅ License gate already implemented with cache + circuit breaker + grace window
✅ mDNS disabled in container environments (CHORUS_MDNS_ENABLED=false)
✅ Connection rate limiting (5 dials/sec, 16 concurrent DHT queries)
✅ Connection manager with watermarks (32 low, 128 high)
✅ AutoNAT enabled for container networking

MEDIUM-RISK FIXES (Next Priority):
✅ Assignment merge layer with HTTP/file config + SIGHUP reload
✅ Runtime configuration system with WHOOSH assignment API support
✅ Election stability windows to prevent churn:
  - CHORUS_ELECTION_MIN_TERM=30s (minimum time between elections)
  - CHORUS_LEADER_MIN_TERM=45s (minimum time before challenging healthy leader)
✅ Bootstrap pool JSON support with priority sorting and join stagger

NEW FEATURES:
- Runtime config system with assignment overrides from WHOOSH
- SIGHUP reload handler for live configuration updates
- JSON bootstrap configuration with peer metadata (region, roles, priority)
- Configurable election stability windows with environment variables
- Multi-format bootstrap support: Assignment → JSON → CSV

FILES MODIFIED:
- pkg/config/assignment.go (NEW): Runtime assignment merge system
- docker/bootstrap.json (NEW): Example JSON bootstrap configuration
- pkg/election/election.go: Added stability windows and churn prevention
- internal/runtime/shared.go: Integrated assignment loading and conditional mDNS
- p2p/node.go: Added connection management and rate limiting
- pkg/config/hybrid_config.go: Added rate limiting configuration fields
- docker/docker-compose.yml: Updated environment variables and configs
- README.md: Updated status table with scaling milestone

This implementation enables wave-based autoscaling without system collapse,
addressing all scaling concerns from WHOOSH issue #7.

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

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

pkg/election/election.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"log"
 	"math/rand"
+	"os"
 	"sync"
 	"time"
 
@@ -102,6 +103,11 @@ type ElectionManager struct {
 	onAdminChanged     func(oldAdmin, newAdmin string)
 	onElectionComplete func(winner string)
 
+	// Stability window to prevent election churn (Medium-risk fix 2.1)
+	lastElectionTime    time.Time
+	electionStabilityWindow time.Duration
+	leaderStabilityWindow   time.Duration
+
 	startTime time.Time
 }
 
@@ -137,6 +143,10 @@ func NewElectionManager(
 		votes:           make(map[string]string),
 		electionTrigger: make(chan ElectionTrigger, 10),
 		startTime:       time.Now(),
+
+		// Initialize stability windows (as per WHOOSH issue #7)
+		electionStabilityWindow: getElectionStabilityWindow(cfg),
+		leaderStabilityWindow:   getLeaderStabilityWindow(cfg),
 	}
 
 	// Initialize heartbeat manager
@@ -220,11 +230,13 @@ func (em *ElectionManager) Stop() {
 	}
 }
 
-// TriggerElection manually triggers an election
+// TriggerElection manually triggers an election with stability window checks
 func (em *ElectionManager) TriggerElection(trigger ElectionTrigger) {
 	// Check if election already in progress
 	em.mu.RLock()
 	currentState := em.state
+	currentAdmin := em.currentAdmin
+	lastElection := em.lastElectionTime
 	em.mu.RUnlock()
 
 	if currentState != StateIdle {
@@ -232,6 +244,26 @@ func (em *ElectionManager) TriggerElection(trigger ElectionTrigger) {
 		return
 	}
 
+	// Apply stability window to prevent election churn (WHOOSH issue #7)
+	now := time.Now()
+	if !lastElection.IsZero() {
+		timeSinceElection := now.Sub(lastElection)
+
+		// If we have a current admin, check leader stability window
+		if currentAdmin != "" && timeSinceElection < em.leaderStabilityWindow {
+			log.Printf("⏳ Leader stability window active (%.1fs remaining), ignoring trigger: %s",
+				(em.leaderStabilityWindow - timeSinceElection).Seconds(), trigger)
+			return
+		}
+
+		// General election stability window
+		if timeSinceElection < em.electionStabilityWindow {
+			log.Printf("⏳ Election stability window active (%.1fs remaining), ignoring trigger: %s",
+				(em.electionStabilityWindow - timeSinceElection).Seconds(), trigger)
+			return
+		}
+	}
+
 	select {
 	case em.electionTrigger <- trigger:
 		log.Printf("🗳️ Election triggered: %s", trigger)
@@ -442,6 +474,7 @@ func (em *ElectionManager) beginElection(trigger ElectionTrigger) {
 	em.mu.Lock()
 	em.state = StateElecting
 	em.currentTerm++
+	em.lastElectionTime = time.Now() // Record election timestamp for stability window
 	term := em.currentTerm
 	em.candidates = make(map[string]*AdminCandidate)
 	em.votes = make(map[string]string)
@@ -1119,3 +1152,43 @@ func (hm *HeartbeatManager) GetHeartbeatStatus() map[string]interface{} {
 
 	return status
 }
+
+// Helper functions for stability window configuration
+
+// getElectionStabilityWindow gets the minimum time between elections
+func getElectionStabilityWindow(cfg *config.Config) time.Duration {
+	// Try to get from environment or use default
+	if stability := os.Getenv("CHORUS_ELECTION_MIN_TERM"); stability != "" {
+		if duration, err := time.ParseDuration(stability); err == nil {
+			return duration
+		}
+	}
+
+	// Try to get from config structure if it exists
+	if cfg.Security.ElectionConfig.DiscoveryTimeout > 0 {
+		// Use double the discovery timeout as default stability window
+		return cfg.Security.ElectionConfig.DiscoveryTimeout * 2
+	}
+
+	// Default fallback
+	return 30 * time.Second
+}
+
+// getLeaderStabilityWindow gets the minimum time before challenging a healthy leader
+func getLeaderStabilityWindow(cfg *config.Config) time.Duration {
+	// Try to get from environment or use default
+	if stability := os.Getenv("CHORUS_LEADER_MIN_TERM"); stability != "" {
+		if duration, err := time.ParseDuration(stability); err == nil {
+			return duration
+		}
+	}
+
+	// Try to get from config structure if it exists
+	if cfg.Security.ElectionConfig.HeartbeatTimeout > 0 {
+		// Use 3x heartbeat timeout as default leader stability
+		return cfg.Security.ElectionConfig.HeartbeatTimeout * 3
+	}
+
+	// Default fallback
+	return 45 * time.Second
+}