[feat](trx-rs): add build/install script and systemd user services

Provide a one-shot installer and matching systemd *user* units so the
server and client can be built, installed system-wide, and run in the
background without hand-rolled steps.

- script/install.sh: builds all three binaries (trx-server, trx-client,
  trx-configurator) in release mode and installs them to /usr/local/bin
  (configurable via --prefix/--bindir/PREFIX, sudo only when the target
  is not writable). Seeds ~/.config/trx-rs/trx-rs.toml from the example
  without ever overwriting existing config, then installs the user units
  with @BINDIR@ substituted to the real path and runs daemon-reload.
  Flags: --no-sdr, --no-build, --no-systemd, --enable-now.
- script/uninstall.sh: stops/disables the units, removes them and the
  binaries; keeps config unless --purge.
- packaging/systemd/{trx-server,trx-client}.service: user units reading
  the combined config at ~/.config/trx-rs/trx-rs.toml. The client softly
  depends on the server (Wants/After). KillSignal=SIGINT matches how the
  binaries shut down cleanly (SIGTERM is not handled).
- README: new "Install (optional, Linux + systemd)" section.

The web UI assets are embedded in the binary, so an install needs only
the binaries plus a config file — no data directory to ship.

Signed-off-by: Stan Grams <sjg@haxx.space>

script/uninstall.sh

@@ -0,0 +1,86 @@
+#!/usr/bin/env bash
+# SPDX-FileCopyrightText: 2026 Stan Grams <sjg@haxx.space>
+#
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
+# Reverse script/install.sh: stop and remove the systemd user services and the
+# installed binaries. User config (~/.config/trx-rs) is left in place unless
+# --purge is given.
+
+set -euo pipefail
+
+BINARIES=(trx-server trx-client trx-configurator)
+
+PREFIX="${PREFIX:-/usr/local}"
+BINDIR="${BINDIR:-}"
+PURGE=0
+
+CONFIG_DIR="${XDG_CONFIG_HOME:-$HOME/.config}/trx-rs"
+UNIT_DIR="${XDG_CONFIG_HOME:-$HOME/.config}/systemd/user"
+
+usage() {
+    cat <<EOF
+Usage: script/uninstall.sh [options]
+
+Options:
+  --prefix DIR   Install prefix binaries were installed under (default: /usr/local)
+  --bindir DIR   Directory binaries were installed to (overrides --prefix)
+  --purge        Also delete the user config directory ($CONFIG_DIR)
+  -h, --help     Show this help
+EOF
+}
+
+while [ $# -gt 0 ]; do
+    case "$1" in
+        --prefix) PREFIX="$2"; shift 2 ;;
+        --bindir) BINDIR="$2"; shift 2 ;;
+        --purge) PURGE=1; shift ;;
+        -h|--help) usage; exit 0 ;;
+        *) echo "error: unknown option '$1'" >&2; usage >&2; exit 2 ;;
+    esac
+done
+
+[ -n "$BINDIR" ] || BINDIR="$PREFIX/bin"
+
+log() { printf '\033[1;32m==>\033[0m %s\n' "$*"; }
+
+need_sudo() {
+    local dir="$1"
+    while [ ! -e "$dir" ]; do dir="$(dirname "$dir")"; done
+    [ -w "$dir" ] && return 1 || return 0
+}
+
+# --- Stop and remove user services -----------------------------------------
+if command -v systemctl >/dev/null 2>&1; then
+    log "Stopping and disabling user services…"
+    systemctl --user disable --now trx-client.service trx-server.service 2>/dev/null || true
+fi
+for unit in trx-client trx-server; do
+    if [ -e "$UNIT_DIR/$unit.service" ]; then
+        rm -f "$UNIT_DIR/$unit.service"
+        log "removed $UNIT_DIR/$unit.service"
+    fi
+done
+if command -v systemctl >/dev/null 2>&1; then
+    systemctl --user daemon-reload || true
+fi
+
+# --- Remove binaries --------------------------------------------------------
+SUDO=""
+if need_sudo "$BINDIR"; then SUDO="sudo"; fi
+for b in "${BINARIES[@]}"; do
+    if [ -e "$BINDIR/$b" ]; then
+        $SUDO rm -f "$BINDIR/$b"
+        log "removed $BINDIR/$b"
+    fi
+done
+
+# --- Optionally purge config ------------------------------------------------
+if [ "$PURGE" -eq 1 ]; then
+    rm -rf "$CONFIG_DIR"
+    log "purged $CONFIG_DIR"
+else
+    log "Left config in place: $CONFIG_DIR (use --purge to delete)"
+fi
+
+log "Done."