fix(fish): guard nvim aliases and add eza fallbacks

Guard vim/vi → nvim aliases with type -q nvim check so they only
activate when nvim is installed. Add ls/ll/l/lsa fallbacks when eza
is not installed. Add brew shellenv fish eval in config.fish.

config/fish/alias.fish

@@ -1,7 +1,9 @@
 # Set aliases for fish shell
 
-alias vim='nvim'
-alias vi='nvim'
+if type -q nvim
+    alias vim='nvim'
+    alias vi='nvim'
+end
 
 # eza aliases if eza is installed
 if type -q eza >/dev/null
@@ -31,6 +33,19 @@ if type -q eza >/dev/null
     function l --wraps='eza_git' --description eza
         eza_git $argv
     end
+else
+    function ls --description 'ls (system fallback)'
+        command ls $argv
+    end
+    function ll --description 'ls -lh (system fallback)'
+        command ls -lh $argv
+    end
+    function l --description 'ls (system fallback)'
+        command ls $argv
+    end
+    function lsa --description 'ls -lah (system fallback)'
+        command ls -lah $argv
+    end
 end
 
 # Edit fish alias file
@@ -130,4 +145,6 @@ alias x-datetime="date +'%Y-%m-%d %H:%M:%S'"
 alias x-timestamp="date +'%s'"
 
 # Random abbreviations
-abbr --add stats onefetch --nerd-fonts --true-color never
+if type -q onefetch
+    abbr --add stats onefetch --nerd-fonts --true-color never
+end

config/fish/config.fish

@@ -52,3 +52,4 @@ source ~/.orbstack/shell/init2.fish 2>/dev/null || :
 if status is-interactive; and not set -q GITHUB_TOKEN
     echo "Warning: GITHUB_TOKEN is not set" >&2
 end
+eval "$(/opt/homebrew/bin/brew shellenv fish)"