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/db/retention.go

@@ -0,0 +1,41 @@
+package db
+
+import (
+	"time"
+
+	"crypto-miner-server/internal/models"
+)
+
+// PurgeHashrateSamplesBefore deletes samples older than cutoff.
+func (d *Database) PurgeHashrateSamplesBefore(cutoff time.Time) (int64, error) {
+	res, err := d.Exec("DELETE FROM hashrate_samples WHERE timestamp < ?", cutoff)
+	if err != nil {
+		return 0, err
+	}
+	return res.RowsAffected()
+}
+
+// ListBuildsOlderThan returns build records created before cutoff.
+func (d *Database) ListBuildsOlderThan(cutoff time.Time) ([]*models.BuildRecord, error) {
+	rows, err := d.Query(`SELECT id, worker_name, server_url, wallet, threads, file_size, file_path, created_at, pool_host, pool_port, pool_tls, pool_pass FROM builds WHERE created_at < ?`, cutoff)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var out []*models.BuildRecord
+	for rows.Next() {
+		b := &models.BuildRecord{}
+		if err := rows.Scan(&b.ID, &b.WorkerName, &b.ServerURL, &b.Wallet, &b.Threads, &b.FileSize, &b.FilePath, &b.CreatedAt,
+			&b.PoolHost, &b.PoolPort, &b.PoolTLS, &b.PoolPass); err != nil {
+			return nil, err
+		}
+		out = append(out, b)
+	}
+	return out, nil
+}
+
+// DeleteBuild removes a build record by id.
+func (d *Database) DeleteBuild(id string) error {
+	_, err := d.Exec("DELETE FROM builds WHERE id = ?", id)
+	return err
+}