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>

files/sway-headless.service

@@ -10,11 +10,21 @@ Type=simple
 
 # Tell wlroots to use the headless backend (no DRM master needed) and skip
 # libinput device probing — there are no input devices on a real headless box.
-# The Vulkan renderer is preferred on NVIDIA + handles NVENC capture cleanly;
-# wlroots falls back to GLES2 automatically if Vulkan isn't usable.
+#
+# GLES2 renderer: the Vulkan backend strictly requires
+# VK_EXT_external_memory_dma_buf, which the proprietary NVIDIA driver
+# doesn't expose on every build (esp. data-center / -server branches). GLES2
+# is universally available and Sunshine's capture path uses its own dma-buf
+# flow, so we don't lose hardware acceleration.
 Environment=WLR_BACKENDS=headless
 Environment=WLR_LIBINPUT_NO_DEVICES=1
-Environment=WLR_RENDERER=vulkan
+# Pixman (software) renderer. The GLES2 path needs a GBM-allocated framebuffer,
+# which fails on the proprietary NVIDIA driver: its GBM bridge doesn't permit
+# unprivileged CREATE_DUMB even on render nodes (Mesa drivers do). The trade-
+# off: Sunshine's wlr-screencopy then takes the shm path and uses libx264
+# software encoding. For NVENC on NVIDIA cloud GPUs, sunshine should be
+# pointed at a virtual KMS connector (vkms or Xorg+Dummy) instead of wlroots.
+Environment=WLR_RENDERER=pixman
 Environment=XDG_SESSION_TYPE=wayland
 
 ExecStart=/usr/bin/sway --config %h/.config/sway/config-headless --unsupported-gpu