docs: record what firmware fixed, and what it turns out not to fix

The motd was the worst of it — it told anyone logging in that "WiFi and
Bluetooth work with the firmware Fedora ships", which is precisely backwards for
the onboard adapter, and pointed at a Windows partition this machine no longer
has.

What the blobs did fix, verified: the GPU initialises, ADSP/CDSP/SLPI all run,
sensors appear as IIO devices, venus registers /dev/video0-3.

What they did not, and why, so nobody repeats the search:

Onboard WiFi is loaded by the modem — wlan*mdsp* is the WLAN Modem DSP — so
ath10k_snoc binds and then waits silently on a QMI service that never arrives.
The modem boots and dies at "RF stuck in QLINK start state", the RF front-end,
which is board-specific wiring in a way the SoC-level blobs are not. These are
Qualcomm *reference* drivers; good enough for the GPU and DSPs, evidently not
for this machine's radio. Three plausible fixes that do not work are recorded
too: rmtfs (correct to enable, does not help), the _nm firmware variants
(rejected at PBL), and unplugging the USB dongle (different bus entirely — it
was never competing).

Audio gets further than expected. The codec answers over SLIMbus with its chip
id, so hardware and ADSP are fine; what fails is the codec's SoundWire block
declaring two data-in ports where the controller expects six. That is a kernel
mismatch and needs a kernel change.

Also record the mesa caveat properly: the GPU works, but freedreno's EGL path
segfaults gnome-shell into a login loop, and LIBGL_ALWAYS_SOFTWARE does nothing
because mutter uses EGL. MESA_LOADER_DRIVER_OVERRIDE=kms_swrast is what works.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XWRjNJMistCy6ngXH5aJLS

overlay/etc/motd.d/c630.in

@@ -1,7 +1,11 @@
 
   Fedora @FEDORA_RELEASE@ for the @DEVICE_DESC@  (built @BUILD_DATE@ from @BUILD_REF@)
 
-  WiFi and Bluetooth work with the firmware Fedora ships. Accelerated
-  graphics, audio, the sensor hub and video decode all need per-model blobs
-  from the Windows partition — run `sudo c630-firmware` once to extract them.
+  No per-model Qualcomm firmware ships in this image — it is not
+  redistributable. Supply it to get accelerated graphics, audio, the sensor
+  hub and hardware video decode: see docs/firmware.md, or run
+  `sudo c630-firmware` if this machine still has its Windows partition.
+
+  Onboard WiFi additionally needs modem firmware that no public source
+  provides. Use a USB dongle or tether a phone over USB.