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/10-input-and-cursor.kdl

@@ -0,0 +1,44 @@
+// Outputs (example - disabled by default)
+// Run `niri msg outputs` inside a niri session to see connector names and modes.
+// Then edit and uncomment this block to pin a specific monitor layout.
+
+// ============================================================================
+// INPUT
+// ============================================================================
+
+input {
+    keyboard {
+        xkb {
+            layout "us"
+        }
+        repeat-delay 400
+        repeat-rate 50
+    }
+    touchpad {
+        natural-scroll
+        tap
+        tap-button-map "left-right-middle"
+        accel-speed 1.0
+    }
+
+    tablet {
+        map-to-output "eDP-1"
+    }
+
+    touch {
+        map-to-output "eDP-1"
+    }
+   
+    mod-key "Super"
+    mod-key-nested "Alt"
+}
+
+gestures {
+
+}
+
+cursor {
+    xcursor-theme "capitaine-cursors-light"
+    xcursor-size 24
+    hide-when-typing
+}