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>

conf.d/abbr.fish

@@ -65,6 +65,21 @@ abbr -a ag. antigravity .
 abbr -a :q kitty @ close-window # Kitty (Closes the active split/pane)
 abbr -a :Q kitty @ close-tab # Kitty (Closes the whole tab)
 
+######### Alternates ##########
+### ls alternates
+# List all files
+abbr -a l ls
+# List all files by size
+abbr -a lS lss
+# List all files by reverse modified time
+abbr -a lsR lsr
+# List by extension
+abbr -a lX lx
+# Tree listing (depth 2)
+abbr -a lT lt
+# Full tree listing
+abbr -a lsT lstree
+
 # Window Creation (OS Windows)
 # abbr -a :w wezterm cli spawn --new-window # WezTerm
 abbr -a :w kitty @ launch --type=os-window # Kitty
@@ -217,4 +232,3 @@ abbr -a scr 'systemctl restart'
 abbr -a ssct 'sudo systemctl status'
 abbr -a sscs 'sudo systemctl start'
 abbr -a sscr 'sudo systemctl restart'
-