feat(arch-layer,scripts): linux-gated desktop configs + package install scripts

niri (exact_config.d, scripts), noctalia (plugins excluded — runtime
state with embedded token), fontconfig, mimeapps.list,
niri-dynamic-workspaces, systemd user unit files (enable-state not
managed; only nirinit enabled by run_once), niri-launch vendored from
/usr/bin (unowned hand-written script, shellcheck warnings pre-existing).

Scripts: packages (pacman --needed + paru, brew on darwin, root-safe,
keyed on packages.yaml hash), gh extensions (idempotent), user services
(linux), post (tpm clone, bat cache, fc-cache). All shellcheck-clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

dot_config/niri/scripts/executable_niri-focus.sh

@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+# Cascade focus: window → occupied workspace → monitor (cycles at edges)
+# Skips the trailing empty workspace — jumps to the monitor instead.
+# usage: niri-focus.sh up|down
+set -euo pipefail
+dir="${1:?usage: niri-focus.sh up|down}"
+opp=$([ "$dir" = down ] && echo up || echo down)
+
+out() { niri msg --json focused-output | jq -r '.name // "none"'; }
+win() { niri msg --json focused-window | jq -r '.id // "none"'; }
+
+# 1) window within the column
+w0=$(win); niri msg action "focus-window-$dir" >/dev/null 2>&1 || true
+[ "$(win)" != "$w0" ] && exit 0
+
+# 2) occupied workspace in that direction (skip the empty trailing one)
+wss=$(niri msg --json workspaces)
+wins=$(niri msg --json windows)
+cwsid=$(jq -r 'map(select(.is_focused)) | .[0].id' <<<"$wss")
+real_neighbor=$(jq -n --argjson wss "$wss" --argjson wins "$wins" \
+  --argjson cwsid "$cwsid" --arg dir "$dir" '
+  ($wss[] | select(.id==$cwsid)) as $c
+  | [ $wss[]
+      | select(.output==$c.output)
+      | select(if $dir=="down" then .idx>$c.idx else .idx<$c.idx end)
+      | .id as $wid
+      | select([$wins[] | select(.workspace_id==$wid)] | length > 0) ]
+  | length > 0')
+
+if [ "$real_neighbor" = "true" ]; then
+  niri msg action "focus-workspace-$dir" >/dev/null 2>&1 || true
+  exit 0
+fi
+
+# 3) adjacent monitor… or wrap to the far-end monitor
+o0=$(out); niri msg action "focus-monitor-$dir" >/dev/null 2>&1 || true
+[ "$(out)" != "$o0" ] && exit 0
+while :; do
+  prev=$(out)
+  niri msg action "focus-monitor-$opp" >/dev/null 2>&1 || true
+  [ "$(out)" = "$prev" ] && break
+done