feat: weighted random routing + mode switching + EWMA smoothing + stale eviction

- Weighted random routing (math/rand/v2 per-goroutine ChaCha8)
- PUT /api/route/mode for runtime mode switch (best / weighted_random)
- EWMA score smoothing (configurable smoothing_factor, default 0.3)
- Periodic stale node eviction (5 min threshold, 60s interval)
- Non-blocking WS broadcast (per-client buffered channel + writePump)
- Background rate limiter cleanup goroutine
- In-memory trunk gateway cache (zero disk I/O in hot path)
- Configurable load_avg multiplier (default 50.0, backward compat)
- UI mode indicator + admin Switch button in dashboard
- 42 tests: weighted random, mode switching, EWMA, eviction, API integration

internal/config/manager.go

@@ -30,6 +30,8 @@ type ScoringConfig struct {
 	IdleCPUMin            float64        `json:"idle_cpu_min"`
 	CallFailureRateLethal float64        `json:"call_failure_rate_lethal"`
 	Weights               ScoringWeights `json:"weights"`
+	SmoothingFactor       float64        `json:"smoothing_factor"`        // 0 = без сглаживания, 0.3 = рекомендуемый EWMA
+	LoadAvgMultiplier     float64        `json:"load_avg_multiplier"`     // множитель load_avg → score (стандартный 50)
 }
 
 // TLSConfig — настройки HTTPS.
@@ -97,6 +99,7 @@ type Config struct {
 	RateLimit         RateLimitConfig `json:"rate_limit"`
 	Log               LogConfig       `json:"log"`
 	ESL               ESLConfig       `json:"esl"`
+	BalanceMode       string          `json:"balance_mode"` // "best" | "weighted_random"
 }
 
 // Validate проверяет корректность всех полей конфига.
@@ -125,6 +128,12 @@ func (c *Config) Validate() error {
 	if c.Scoring.CallFailureRateLethal < 0 || c.Scoring.CallFailureRateLethal > 100 {
 		errs = append(errs, "scoring.call_failure_rate_lethal должен быть 0..100")
 	}
+	if c.Scoring.SmoothingFactor < 0 || c.Scoring.SmoothingFactor > 1 {
+		errs = append(errs, "scoring.smoothing_factor должен быть 0..1")
+	}
+	if c.Scoring.LoadAvgMultiplier < 0 {
+		errs = append(errs, "scoring.load_avg_multiplier должен быть >= 0")
+	}
 
 	w := &c.Scoring.Weights
 	sum := w.CallScore + w.LoadScore + w.IdleScore + w.FailScore
@@ -158,6 +167,13 @@ func (c *Config) Validate() error {
 		errs = append(errs, "log.format должен быть text/json")
 	}
 
+	// Balance mode validation
+	switch c.BalanceMode {
+	case "best", "weighted_random", "":
+	default:
+		errs = append(errs, "balance_mode должен быть best или weighted_random")
+	}
+
 	// ESL validation
 	if c.ESL.Host != "" {
 		if c.ESL.Port <= 0 || c.ESL.Port > 65535 {
@@ -374,6 +390,8 @@ func (m *Manager) createDefaultConfig() error {
 				IdleScore: 0.20,
 				FailScore: 0.10,
 			},
+			SmoothingFactor:   0.3,
+			LoadAvgMultiplier: 50.0,
 		},
 		TLS: TLSConfig{
 			Enabled:  false,
@@ -397,6 +415,7 @@ func (m *Manager) createDefaultConfig() error {
 			SofiaProfile:  "external",
 			GatewayPrefix: "pulse",
 		},
+		BalanceMode: "weighted_random",
 	}
 
 	return m.SaveConfig(&cfg)