feat(dotfiles): import env layer as stow-style packages with deploy.sh

Import Dankware's environment layer into the repo as home-relative package
trees (niri, gtk-3/4, ghostty, alacritty, fish, zsh, bash, profile,
systemd-user, dconf). scripts/deploy.sh implements stow-equivalent semantics
(check|adopt|sync modes): identical files adopt to symlinks, new files link,
divergent files quarantine-and-replace under .quarantine/<host>/<ts>/ (gitignored).
zz-<hostname> override packages deploy last with override semantics.

Secrets never enter git: GITEA_TOKEN moved from .zshrc into untracked
~/.config/environment.d/secrets.env (0600); tracked .zshrc sources it
guarded. core.hooksPath armed by deploy.sh so the pre-commit secret gate is
live on every machine that deploys.

dotfiles/niri/.config/niri/cfg/layout.kdl

@@ -0,0 +1,14 @@
+    layout {
+        gaps 16 // Gap between windows
+        center-focused-column "never" // Don’t auto-center focused column
+
+        background-color "transparent" // <- needed for noctalia-shell to set wallpaper
+
+        preset-column-widths {
+            proportion 0.33333
+            proportion 0.5
+            proportion 0.66667
+        }
+
+        struts {}
+    }