Add fleet ops dashboard, Calibrate enforcement, and dead-code cleanup.

Ship live alerts, pool status, AI monitor, remote agent commands, build manager, and uninstall flow; wire Calibrate settings (WS ping, pool traffic log, retention limits) at runtime and exclude server/data from git.

server/internal/maintenance/retention.go

@@ -0,0 +1,58 @@
+package maintenance
+
+import (
+	"log"
+	"os"
+	"path/filepath"
+	"time"
+
+	"crypto-miner-server/internal/db"
+)
+
+// StartRetentionJobs purges old stats and build artifacts on an interval.
+func StartRetentionJobs(database *db.Database, dataDir string, statsHours, buildDays int) {
+	if statsHours <= 0 && buildDays <= 0 {
+		return
+	}
+	go func() {
+		runRetention(database, dataDir, statsHours, buildDays)
+		ticker := time.NewTicker(6 * time.Hour)
+		defer ticker.Stop()
+		for range ticker.C {
+			runRetention(database, dataDir, statsHours, buildDays)
+		}
+	}()
+}
+
+func runRetention(database *db.Database, dataDir string, statsHours, buildDays int) {
+	if statsHours > 0 {
+		cutoff := time.Now().Add(-time.Duration(statsHours) * time.Hour)
+		n, err := database.PurgeHashrateSamplesBefore(cutoff)
+		if err != nil {
+			log.Printf("[Retention] hashrate purge failed: %v", err)
+		} else if n > 0 {
+			log.Printf("[Retention] purged %d hashrate samples older than %dh", n, statsHours)
+		}
+	}
+	if buildDays > 0 {
+		cutoff := time.Now().Add(-time.Duration(buildDays) * 24 * time.Hour)
+		builds, err := database.ListBuildsOlderThan(cutoff)
+		if err != nil {
+			log.Printf("[Retention] build list failed: %v", err)
+			return
+		}
+		for _, b := range builds {
+			if b.FilePath != "" {
+				dir := filepath.Dir(b.FilePath)
+				_ = os.RemoveAll(dir)
+			} else {
+				_ = os.RemoveAll(filepath.Join(dataDir, "builds", b.ID))
+			}
+			if err := database.DeleteBuild(b.ID); err != nil {
+				log.Printf("[Retention] delete build %s: %v", b.ID, err)
+			} else {
+				log.Printf("[Retention] removed build %s (%s)", b.ID, b.WorkerName)
+			}
+		}
+	}
+}