Add runtime status checker + headless/X11 docs; distro-support refinements

- status.sh: runtime health check (service state, boot wiring, display backend auto-detect, encoder, ports, web UI, /dev/uinput, pairing) ending in a g2g verdict or concrete TODO list

- docs: TROUBLESHOOTING §12 (headless graphical-session.target boot trap) + §13 (X11/NVENC path & stale wlr drop-in env conflict); ARCHITECTURE capture-backend comparison; FOLLOWUPS P3 (installer X11/Ubuntu support); README diagnostics pointer

- lib/{config,packages,permissions,service}.sh, files/sway-headless.service: in-progress Debian/Ubuntu + headless support refinements

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/config.sh

@@ -70,10 +70,10 @@ $encoder_block
 min_threads = 4
 
 # Audio sink is intentionally left unset so Sunshine auto-detects the default
-# PulseAudio/PipeWire sink and creates its virtual `sink-sunshine-stereo`.
+# PulseAudio/PipeWire sink and creates its virtual 'sink-sunshine-stereo'.
 # Hard-coding audio_sink = pulse here breaks capture: Sunshine treats it as a
 # literal sink name, can't resolve its monitor source, and pa_simple_new()
-# fails with "Invalid argument" → no audio in the stream.
+# fails with "Invalid argument" -> no audio in the stream.
 
 # Keyboard / mouse / gamepad pass-through via /dev/uinput.
 # (Requires user to be in the 'input' group; install.sh handles this.)