refactor: replace lazy zoxide with eager init and add fd-based directory discovery

- Switch from lazy-loaded z/zi to eager zoxide initialization in config.fish
- Alias cd to use zoxide for automatic frecency tracking
- Add Alt+D: discover directories from git root/cwd with fd+fzf (no gitignore)
- Add Alt+Shift+D: discover directories from HOME with fd+fzf (depth 5)

home/dot_config/fish/functions/_fzf_discover_home.fish

@@ -0,0 +1,18 @@
+# Directory finder starting from HOME with fd + fzf (shows all directories)
+function _fzf_discover_home --description "Alt+Shift+D: Discover directories from HOME with fd+fzf"
+    set -l selected (
+        fd --type d --hidden --no-ignore --max-depth 5 \
+            --exclude .git --exclude node_modules \
+            . "$HOME" | \
+        fzf --height=50% \
+            --preview="lsd -1 --color=always --icon=always {}" \
+            --preview-window=right,40% \
+            --prompt="🏠 Home > " \
+            --header="Searching from: $HOME (max depth 5, all dirs)"
+    )
+
+    if test -n "$selected"
+        cd "$selected"
+        commandline -f repaint
+    end
+end