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/noctalia/colors.json

@@ -0,0 +1,25 @@
+{
+  "mPrimary": "#a398b3",
+  "mOnPrimary": "#100f13",
+
+  "mSecondary": "#9c8da5",
+  "mOnSecondary": "#1e1c22",
+
+  "mTertiary": "#a18fa3",
+  "mOnTertiary": "#1e1c22",
+
+  "mError": "#fd4663",
+  "mOnError": "#1e1c22",
+
+  "mSurface": "#1e1c21",
+  "mOnSurface": "#f2f2f3",
+
+  "mSurfaceVariant": "#322f37",
+  "mOnSurfaceVariant": "#b2b0b5",
+  
+  "mOutline": "#6a6670",
+  "mShadow": "#1e1c21",
+
+  "mHover": "#a18fa3",
+  "mOnHover": "#1e1c22"
+}