fix(syslog-server): rotate /var/log/remote so the disk can't fill (INFRA-11)

The collector's remote-syslog spool had no rotation, so each gateway's
/var/log/remote/<host>/<host>.log grew unbounded. Low risk at the old
~109 events/day, but the gateways now forward ~60k/day. CloudWatch (90d)
is the system of record; the local files are only a CW-agent spool, so
keep a short 7-day compressed window. copytruncate keeps rsyslog's open
dynaFile handles valid (truncate in place).

Applied live already; this codifies it so an instance replacement keeps it
(mirrors the existing netflow-retention timer). Deploying this user-data
change forces an instance replacement (userDataCausesReplacement) — the EIP
re-associates and the forwarding target is unchanged, so do it in a window.

lib/syslog-server-stack.ts

@@ -115,6 +115,22 @@ export class SyslogServerStack extends cdk.Stack {
       "systemctl enable rsyslog",
       "systemctl restart rsyslog",
       "",
+      "# ── Rotate /var/log/remote so it can't grow unbounded ──",
+      "# CloudWatch (90d) is the system of record; these local files are just a",
+      "# spool for the CW agent, so keep only a short window. copytruncate keeps",
+      "# rsyslog's open dynaFile handles valid (truncate in place, same inode).",
+      "cat > /etc/logrotate.d/remote-syslog <<'EOF'",
+      "/var/log/remote/*/*.log {",
+      "    daily",
+      "    rotate 7",
+      "    compress",
+      "    delaycompress",
+      "    missingok",
+      "    notifempty",
+      "    copytruncate",
+      "}",
+      "EOF",
+      "",
       "# ── CloudWatch agent: ship /var/log/remote/**/*.log to unifi-syslog ──",
       "dnf install -y amazon-cloudwatch-agent",
       "cat > /opt/aws/amazon-cloudwatch-agent/etc/amazon-cloudwatch-agent.json <<'EOF'",