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/60-animations.kdl

@@ -0,0 +1,32 @@
+// ============================================================================
+// ANIMATIONS
+// ============================================================================
+// Tuned to complement quickshell's expressive Material motion curves
+// QS uses ~500ms for main movements, ~400ms enter, ~200ms exit
+
+animations {
+ workspace-switch {
+spring damping-ratio=1.0 stiffness=4000 epsilon=0.0001
+    }
+ window-open                   { 
+        spring damping-ratio=1.0 stiffness=5000 epsilon=0.0001
+    }
+    window-close                  { 
+        spring damping-ratio=1.0 stiffness=6000 epsilon=0.0001 
+    }
+    horizontal-view-movement      { 
+        spring damping-ratio=1.0 stiffness=4500 epsilon=0.0001 
+    }
+    window-movement               { 
+        spring damping-ratio=1.0 stiffness=5000 epsilon=0.0001 
+    }
+    window-resize                 { 
+        spring damping-ratio=1.0 stiffness=5500 epsilon=0.0001 
+    }
+    config-notification-open-close { 
+        spring damping-ratio=1.0 stiffness=5000 epsilon=0.0001 
+    }
+    screenshot-ui-open            { 
+        spring damping-ratio=1.0 stiffness=5000 epsilon=0.0001 
+    }
+}