Untrack a retired niri config that was committed as trash; correct two census rows

The repo still tracked `dotfiles/niri/.config/niri/cfg/.AGENTTRASH/display.kdl.superseded`
— a retired output config committed 2026-10-09, five days before `.gitignore` grew the
`.AGENTTRASH/` rule. Tracked-then-ignored: an ignore rule never reaches an already-tracked
path, so `git rm --cached` is the only repair. The working copy joins the rest of today's
tracked debt.

Found while answering "does this repo still track my noctalia and niri settings", which
also falsified two rows of the census committed yesterday: niri is 9 tracked files, not
12; noctalia is 3 authored files against 2672 files of app state and downloaded catalog,
not 2/0. The page's own classifier command reproduces the new numbers — it never
reproduced the old ones, which is the only reason they were wrong and not merely
different.

Two laws recorded alongside, both from the same probe: `config.kdl`'s
`include "noctalia.kdl"` is not `optional=true`, so a fresh box cannot start niri until
the theme pipeline has run once; and `cfg/display.kdl -> desk-1-home.kdl` is desk state a
fresh box does not receive — by design, but nowhere written down.

Refs #40

dotfiles/niri/.config/niri/cfg/.AGENTTRASH/display.kdl.superseded

@@ -1,21 +0,0 @@
-// ────────────── Output Configuration ──────────────
-output "Samsung Electric Company Odyssey G75F HNTY601056" {
-    mode "3840x2160@60"
-    scale 1
-    transform "normal"
-    position x=0 y=0
-}
-
-output "DP-1" {
-    transform "90"
-    position x=0 y=0
-}
-
-output "DP-3" {
-    transform "270"
-    position x=1200 y=0
-}
-
-output "eDP-1" {
-    // no position — auto-placed to the right of DP-* outputs
-}