feat: add systemd user service for daemon mode

- contrib/teleportfling.service: per-user unit running the headless CLI
  with its own config (~/.config/teleportfling/daemon.json)
- contrib/install-daemon.sh: builds the binary, installs the unit and a
  starter daemon config
- contrib/README.md: install and management instructions
- todo.md: mark --config and daemon items complete

contrib/README.md

@@ -0,0 +1,40 @@
+# Running TeleportFling as a daemon
+
+`teleportfling` (the headless CLI) can run as a per-user systemd service so
+the stream starts automatically with your graphical session.
+
+## Prerequisites
+
+- The binary must be built (the flake dev shell provides all cgo deps).
+- The screen-capture backend needs the session D-Bus and a PipeWire instance,
+  which is why the unit is a *user* service tied to `graphical-session.target`.
+
+## Install
+
+```sh
+./contrib/install-daemon.sh
+```
+
+This:
+
+1. Builds `cmd/teleportfling` and installs it to `~/.local/bin/`.
+2. Installs `contrib/teleportfling.service` as a user unit.
+3. Creates `~/.config/teleportfling/daemon.json` on first run.
+4. Runs `systemctl --user daemon-reload` and enables the service.
+
+## Manage
+
+```sh
+systemctl --user start teleportfling    # start now
+systemctl --user enable teleportfling   # start at login (done by installer)
+systemctl --user status teleportfling   # check status / logs
+journalctl --user -u teleportfling -f   # follow logs
+systemctl --user stop teleportfling     # stop
+```
+
+## Config
+
+The unit passes `--config ~/.config/teleportfling/daemon.json`. Edit that
+file to change name, port, quality, fps, source, audio or announcement, then
+restart the service. Any flags you add to the `ExecStart=` line override the
+file values.

contrib/install-daemon.sh

@@ -0,0 +1,58 @@
+#!/usr/bin/env bash
+# Install teleportfling as a per-user systemd service (daemon mode).
+#
+# Builds the headless binary, places it in ~/.local/bin, installs the user
+# unit from contrib/teleportfling.service, and creates a starter daemon
+# config. Run without sudo:
+#
+#   ./contrib/install-daemon.sh
+#
+# Then start it with:
+#
+#   systemctl --user enable --now teleportfling
+set -euo pipefail
+
+HERE="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+BIN_DIR="${HOME}/.local/bin"
+SERVICE_DIR="${HOME}/.config/systemd/user"
+CONFIG_DIR="${HOME}/.config/teleportfling"
+CONFIG="${CONFIG_DIR}/daemon.json"
+
+echo "Building teleportfling..."
+(cd "${HERE}" && go build -o "${BIN_DIR}/teleportfling" ./cmd/teleportfling)
+
+echo "Installing systemd user unit..."
+mkdir -p "${SERVICE_DIR}"
+install -m 0644 "${HERE}/contrib/teleportfling.service" "${SERVICE_DIR}/teleportfling.service"
+
+if [[ ! -f "${CONFIG}" ]]; then
+    echo "Creating default daemon config at ${CONFIG}..."
+    mkdir -p "${CONFIG_DIR}"
+    cat > "${CONFIG}" <<'EOF'
+{
+  "name": "TeleportFling Daemon",
+  "port": 9756,
+  "quality": 80,
+  "fps": 30,
+  "source": "screen",
+  "audio": true,
+  "stream_index": 0,
+  "announce": true
+}
+EOF
+fi
+
+echo "Reloading systemd and enabling the service..."
+systemctl --user daemon-reload
+systemctl --user enable teleportfling
+
+cat <<EOF
+
+Installed. Start the daemon with:
+    systemctl --user start teleportfling
+
+Check status with:
+    systemctl --user status teleportfling
+
+Edit settings in ${CONFIG} (the service passes it via --config).
+EOF

contrib/teleportfling.service

@@ -0,0 +1,16 @@
+[Unit]
+Description=TeleportFling screen and audio stream sender
+Documentation=https://github.com/fzwoch/obs-teleport
+After=graphical-session.target pipewire.service
+PartOf=graphical-session.target
+
+[Service]
+Type=simple
+ExecStart=%h/.local/bin/teleportfling --config %h/.config/teleportfling/daemon.json
+Restart=on-failure
+RestartSec=2
+# The capture backend needs the session bus and a PipeWire instance.
+Environment=XDG_RUNTIME_DIR=%t
+
+[Install]
+WantedBy=default.target

todo.md

@@ -10,9 +10,12 @@ Backlog of deferred / planned work, tracked outside of milestone milestones.
 - [ ] **Surface runtime errors in the GUI** — capture/encode failures currently
       only hit the log. Show them in the status label (e.g. a denied
       screen-share dialog) so problems are visible without reading logs.
-- [ ] **`--config` flag** — allow the CLI and GUI to point at a custom config
-      path (`teleportfling --config /path/config.json`). Useful for a future
-      daemon or service and for running multiple profiles side by side.
+- [x] **`--config` flag** — the CLI and GUI accept a custom config path
+      (`teleportfling --config /path/config.json`); explicit CLI flags
+      override file values. Used by the systemd daemon unit in contrib/.
+- [x] **Run as a daemon** — `contrib/install-daemon.sh` installs a per-user
+      systemd unit (`contrib/teleportfling.service`) that starts the headless
+      CLI with its own config at `~/.config/teleportfling/daemon.json`.
 
 ## Ideas (not yet scoped)