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/exact_config.d/90-outputs.kdl

@@ -0,0 +1,47 @@
+// ============================================================================
+// OUTPUTS
+// ============================================================================
+//
+// // Apple Display
+// output "Apple Computer Inc StudioDisplay 0x984262A7" {
+//     position x=0 y=0
+//     scale 1.5
+//     layout {
+//         center-focused-column "never"
+//         always-center-single-column true
+//         gaps 8
+//         default-column-width {
+//             proportion 0.75
+//         }
+//         preset-column-widths {
+//             proportion 0.25
+//             proportion 0.5
+//             proportion 0.75
+//         }
+//     }
+// }
+//
+//
+//
+// output "DP-5" {
+//   off
+// }
+//
+//
+output "DP-4" {
+  off
+}
+// ============================================================================
+// OUTPUTS
+// ============================================================================
+// The Studio Display exposes a phantom second connector (DP-4/5/6, varies per
+// boot) whose only mode is 640x480. Connector name and EDID both shift, so it
+// can't be matched in config — this script finds it by mode signature instead.
+// spawn-at-startup "/home/prad/.config/niri/scripts/kill-phantom-display.fish"
+
+
+include "91-internal-display.kdl"
+// include "92-ultrawide.kdl"
+include "93-apple-display.kdl"
+include "94-portable-hdmi.kdl"
+// include "95-portable-usbc.kdl"