refactor: consolidate and expand ls function family

- Upgrade ls to long listing (-l -a) and drop the standalone l and lS functions in favor of abbreviations
- Remove llm (ambiguous name, redundant with ltr)
- Add lsr (reversed time oneline), lss (size-sorted), lD (dirs-only), lx (extension-sorted)
- Enhance ltr with --all and age color-scale gradient
- Wire up ls abbreviations: l, lS, lsR, lX, lT, lsT
- Update README functions table and add Listing abbreviations section

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

functions/ls.fish

@@ -1,12 +1,12 @@
 # Copyright (C) 2026 Rootiest
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-function ls --description 'List files'
+function ls --description 'List all files'
     if which eza >/dev/null 2>&1
-        eza --oneline --icons --color=auto --hyperlink $argv
+        eza -l -a --icons --color=auto --hyperlink $argv
 
     else if which lsd >/dev/null 2>&1
-        lsd --hyperlink=auto $argv
+        lsd -l -a --hyperlink=auto $argv
     else
         command ls --color=auto $argv
     end