docs(niri): the ultrawide's refresh ceiling was a typo, not a limit

The page asserted the Sceptre M34's EDID tops out at 180 Hz. Measured on blankpad
after the merge, `niri msg outputs` lists 3440x1440@239.998 — the claim was false
in main, and it was load-bearing: it is the reason nobody questioned the profile
while the panel ran at 60 Hz for weeks. The real defect was one character: the
profile asked for 239.999, the panel offers 239.998, and niri matches mode strings
verbatim, falling back to *preferred* without failing.

Corrected to the measured mode list, and the deployed 180 is now documented as a
deliberate choice (the link is trained at x8 32.0 GT/s against a max of x16 and the
display engine throws EINVAL), so the next reader neither "restores 240" blind nor
re-pins 180 as a hardware ceiling. The kdl profile comment carries the same facts at
the point of edit, because that is where the next change to this mode gets typed.

Refs #60

dotfiles/zz-blankpad/niri/.config/niri/cfg/desk-1-home.kdl

@@ -7,10 +7,14 @@
 // requires: Lenovo Group Limited 0x40A9 Unknown
 // optional: HDMI-A-1 (PM1601, dock-dependent)
 
-// This panel's EDID tops out at 3440x1440@180 (read live from niri: no 240 Hz mode
-// exists). Ask for a mode the panel does not offer and niri does not fail — it logs
-// "could not be found, falling back to preferred" and drops to 60 Hz on every
-// reconnect. Keep 180 here unless a re-read EDID says otherwise.
+// The panel offers 3440x1440@239.998 as well as @180.000 (`niri msg outputs`, 2026-10-21), and
+// 180 is driven DELIBERATELY: the link trained at x8 32.0 GT/s against a max of x16 and the
+// display engine is throwing DMCUB errors with EINVAL page flips after s2idle, so the 240-class
+// mode stays undriven until a reboot clears that state. niri matches mode strings VERBATIM and
+// does not round: "@239.999" is not "@239.998", and a mode it cannot find does not fail — it
+// logs "could not be found, falling back to preferred" and drops the panel to 60 Hz on every
+// reconnect, which is how this desk ran for weeks. Copy the string from `niri msg outputs`.
+// Reasoning and triage: omp-docs/tools/niri/displays.md ("The config pattern", rules 4 and 5).
 output "Sceptre Tech Inc Sceptre M34 Unknown" {
     mode "3440x1440@180.000"
     scale 1