mbproxy: cross-platform support — Linux/systemd alongside Windows

Make the service build, run, and install on Linux as a first-class
target while keeping the Windows Service + Event Log behaviour intact.

- Build: drop the hardcoded win-x64 RID — single-file publish now works
  for any RID. publish.ps1 gains -Rid; new publish.sh for Linux hosts.
- Diagnostics: DiagnosticSinkSelector picks the Error+ sink per host —
  Windows Event Log under the SCM, local syslog under systemd
  (Serilog.Sinks.SyslogMessages), none for interactive runs. The
  EventLog truncation helper is extracted so it is testable cross-OS.
- Host: Program.cs registers AddSystemd() alongside AddWindowsService().
- Config: a RID-conditioned appsettings template ships Windows or Unix
  paths; both templates are schema-validated by a test.
- Install: systemd unit (Type=exec) plus install.sh / uninstall.sh.
  Also fixes two cross-platform bugs found while testing: install.ps1
  and uninstall.ps1 used New-EventLog / Remove-EventLog (absent in
  PowerShell 7), and the E2E sim launcher hardcoded Windows venv paths.
- Docs updated across README, CLAUDE.md, and docs/ for dual-platform.

413 tests pass on Windows; 374 (all non-simulator) on Linux.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mbproxy/install/uninstall.sh

@@ -0,0 +1,85 @@
+#!/usr/bin/env bash
+#
+# uninstall.sh — remove the mbproxy service from a Linux / systemd host.
+#
+# The Linux counterpart of uninstall.ps1. Stops and disables the service,
+# removes the systemd unit and installed files, and (unless --keep-config)
+# removes the config directory. Log files are always preserved: they are moved
+# to a timestamped archive so post-uninstall diagnostics remain accessible.
+#
+# Usage:
+#   sudo ./uninstall.sh [--keep-config] [--keep-user]
+#
+#   --keep-config   leave /etc/mbproxy/appsettings.json in place.
+#   --keep-user     leave the mbproxy service account in place.
+#
+set -euo pipefail
+
+SERVICE_NAME="mbproxy"
+SERVICE_USER="mbproxy"
+INSTALL_DIR="/opt/mbproxy"
+CONFIG_DIR="/etc/mbproxy"
+LOG_DIR="/var/log/mbproxy"
+CACHE_DIR="/var/cache/mbproxy"
+UNIT_DEST="/etc/systemd/system/${SERVICE_NAME}.service"
+
+keep_config=0
+keep_user=0
+while [[ $# -gt 0 ]]; do
+    case "$1" in
+        --keep-config) keep_config=1; shift ;;
+        --keep-user)   keep_user=1; shift ;;
+        *)             echo "Unknown argument: $1" >&2; exit 2 ;;
+    esac
+done
+
+if [[ "$(id -u)" -ne 0 ]]; then
+    echo "uninstall.sh must run as root (use sudo)." >&2
+    exit 1
+fi
+
+echo "Uninstalling ${SERVICE_NAME} service..."
+
+# ── 1. Stop + disable the service ────────────────────────────────────────────
+if systemctl list-unit-files "${SERVICE_NAME}.service" >/dev/null 2>&1 \
+   && [[ -n "$(systemctl list-unit-files "${SERVICE_NAME}.service" --no-legend 2>/dev/null)" ]]; then
+    echo "Stopping and disabling '${SERVICE_NAME}'..."
+    systemctl disable --now "$SERVICE_NAME" >/dev/null 2>&1 || true
+fi
+
+# ── 2. Remove the systemd unit ───────────────────────────────────────────────
+if [[ -f "$UNIT_DEST" ]]; then
+    echo "Removing systemd unit '${UNIT_DEST}'..."
+    rm -f "$UNIT_DEST"
+fi
+systemctl daemon-reload
+systemctl reset-failed "$SERVICE_NAME" >/dev/null 2>&1 || true
+
+# ── 3. Archive logs (always preserved, never deleted) ────────────────────────
+if [[ -d "$LOG_DIR" ]]; then
+    timestamp="$(date -u +%Y%m%dT%H%M%SZ)"
+    archive_dir="${LOG_DIR}.archived-${timestamp}"
+    echo "Archiving logs to '${archive_dir}'..."
+    mv "$LOG_DIR" "$archive_dir"
+fi
+
+# ── 4. Remove installed files ────────────────────────────────────────────────
+rm -rf "$INSTALL_DIR" "$CACHE_DIR"
+
+if [[ "$keep_config" -eq 1 ]]; then
+    echo "Keeping config at '${CONFIG_DIR}/appsettings.json' (--keep-config)."
+else
+    rm -rf "$CONFIG_DIR"
+fi
+
+# ── 5. Remove the service account ────────────────────────────────────────────
+if [[ "$keep_user" -eq 0 ]] && id -u "$SERVICE_USER" >/dev/null 2>&1; then
+    echo "Removing service account '${SERVICE_USER}'..."
+    userdel "$SERVICE_USER" 2>/dev/null || true
+fi
+
+echo ""
+echo "Uninstall complete."
+if compgen -G "${LOG_DIR}.archived-*" >/dev/null; then
+    echo "Archived logs: ${LOG_DIR}.archived-*"
+fi