refactor(linux): use @bindir@ placeholder in service template

Both install.sh (PREFIX/bin) and nfpm postinstall (/usr/bin) now
expand the placeholder explicitly, removing the implicit assumption
that the template's hardcoded path matches any particular installer.

Author: cserby

packaging/linux/install.sh

@@ -91,10 +91,10 @@ fi
 SYSTEMD_UNIT_DIR=/usr/lib/systemd/user
 if [ -d "$SYSTEMD_UNIT_DIR" ] || command -v systemctl > /dev/null 2>&1; then
     echo "Installing systemd user unit …"
-    # Rewrite ExecStart to match the actual install prefix. Escape the
-    # replacement string so sed metacharacters (& \ |) in the path are literal.
-    ESCAPED_EXEC="$(printf '%s\n' "${BINDIR}/openlogi-agent" | sed 's|[&\\|]|\\&|g')"
-    sed "s|ExecStart=.*|ExecStart=${ESCAPED_EXEC}|" \
+    # Expand the @BINDIR@ placeholder to match the actual install prefix.
+    # Escape the replacement so sed metacharacters (& \ |) in the path are literal.
+    ESCAPED_BINDIR="$(printf '%s\n' "${BINDIR}" | sed 's|[&\\|]|\\&|g')"
+    sed "s|@BINDIR@|${ESCAPED_BINDIR}|g" \
         "${SCRIPT_DIR}/systemd/openlogi-agent.service" \
         | sudo tee "${SYSTEMD_UNIT_DIR}/openlogi-agent.service" > /dev/null
     # Best-effort daemon-reload for the invoking user so a reinstall picks up

packaging/linux/systemd/openlogi-agent.service

@@ -1,8 +1,10 @@
 # OpenLogi background agent — packaged user unit.
 #
-# This file is installed to /usr/lib/systemd/user/ by the package manager (or
-# install.sh). It is the system-provided template; the agent's launch_at_login
-# setting writes its own copy to $XDG_CONFIG_HOME/systemd/user/ — both coexist,
+# This file is a template — @BINDIR@ is substituted at install time:
+#   - nfpm (.deb/.rpm): postinstall.sh expands it to /usr/bin
+#   - install.sh: expanded to PREFIX/bin (default /usr/local/bin)
+# The agent's launch_at_login setting writes its own copy to
+# $XDG_CONFIG_HOME/systemd/user/ using the current binary path — both coexist,
 # enabling either works.
 #
 # Enable for the current user:
@@ -14,7 +16,7 @@ After=graphical-session.target
 
 [Service]
 Type=simple
-ExecStart=/usr/bin/openlogi-agent
+ExecStart=@BINDIR@/openlogi-agent
 Restart=on-failure
 RestartSec=5