feat(proxy): add generic rsyslog receiver for exposed services

A fail2ban jail running inside a service's own LXC only ever sees this
proxy's tailnet IP as the connection source, so it would end up
banning the proxy itself. Detection needs to stay at the service's
application log; banning needs to happen here, at the edge where
public connections terminate.

Adds a generic imtcp listener (port RSYSLOG_PORT, default 5514) that
routes anything unclaimed by a later 50-<service>.conf into
/var/log/remote/<sender-hostname>.log, plus logrotate with
copytruncate so fail2ban never loses its file descriptor. No
service-specific routing yet — that's one 50-<service>.conf per
service, documented here for the next issue to follow.

Refs #20

proxy/install.sh

@@ -44,6 +44,13 @@ ACME_EMAIL="${ACME_EMAIL:-}"
 # Generate at https://login.tailscale.com/admin/settings/keys
 TS_AUTHKEY="${TS_AUTHKEY:-}"
 
+# rsyslog receiver for exposed services' logs (see "Configuring rsyslog" below).
+RSYSLOG_PORT="${RSYSLOG_PORT:-5514}"
+# Default 0.0.0.0 is fine: UFW's default-deny only opens 80/443 publicly, so
+# this port is reachable exclusively over tailscale0 either way. Override to
+# a specific tailnet IP to shrink the blast radius of log injection instead.
+RSYSLOG_BIND_ADDR="${RSYSLOG_BIND_ADDR:-0.0.0.0}"
+
 main() {
     log_info "=== Proxy Server Deployment (Traefik v3) ==="
 
@@ -75,7 +82,7 @@ main() {
 
     log_info "Installing base packages..."
     sudo apt update -qq
-    sudo apt install -y -qq vim ca-certificates curl gnupg lsb-release fail2ban unattended-upgrades ufw ethtool networkd-dispatcher > /dev/null
+    sudo apt install -y -qq vim ca-certificates curl gnupg lsb-release fail2ban unattended-upgrades ufw ethtool networkd-dispatcher rsyslog > /dev/null
 
     log_info "Installing Tailscale..."
     curl -fsSL https://tailscale.com/install.sh | sh
@@ -174,6 +181,40 @@ EOF
 
     sudo systemctl restart fail2ban
 
+    log_info "Configuring rsyslog receiver for exposed services..."
+    # A fail2ban jail running inside a service's own LXC only ever sees this
+    # proxy's tailnet IP as the source of connections, so it would end up
+    # banning the proxy itself. Detection has to stay where the signal is
+    # (the service's application log); banning has to happen here, at the
+    # edge where public connections actually terminate. Services forward
+    # their logs to this receiver over TCP; adding a new one is a matter of
+    # dropping a 50-<service>.conf here (see proxy/README.md) — nothing else
+    # to touch.
+    sudo mkdir -p /var/log/remote
+    sudo tee /etc/rsyslog.d/10-remote-receiver.conf > /dev/null << EOF
+module(load="imtcp")
+
+\$RuleSet remoteLogs
+\$template RemoteLogPath,"/var/log/remote/%HOSTNAME%.log"
+*.* ?RemoteLogPath
+\$RuleSet RSYSLOG_DefaultRuleset
+
+input(type="imtcp" port="${RSYSLOG_PORT}" address="${RSYSLOG_BIND_ADDR}" ruleset="remoteLogs")
+EOF
+
+    sudo tee /etc/logrotate.d/remote-logs > /dev/null << 'EOF'
+/var/log/remote/*.log {
+    daily
+    rotate 7
+    compress
+    missingok
+    notifempty
+    copytruncate
+}
+EOF
+
+    sudo systemctl restart rsyslog
+
     log_info "Creating Traefik stack under $TRAEFIK_DIR..."
     mkdir -p "$TRAEFIK_DIR/conf.d"