refactor(shell): extract _fish_mkdir_p utility; improve poke output

- Add _fish_mkdir_p: reusable mkdir -p with three output modes:
  --path (default): "Created: ~/full/path/" on one line
  --tree: dimmed existing anchor + cyan tree of newly-created dirs
  --silent: no output
  HOME is substituted with ~ in all output paths
- Refactor poke to delegate to _fish_mkdir_p --tree; removes inline
  mkdir/echo logic and gains ~ substitution and per-dir tree output

functions/poke.fish

@@ -8,10 +8,7 @@ function poke --description 'touch with automatic parent directory creation'
     end
     for _path in $argv
         set -l _dir (dirname $_path)
-        if not test -d $_dir
-            mkdir -p $_dir
-            and echo (set_color --bold cyan)"Created: "(set_color cyan)"$_dir"(set_color normal)
-        end
+        _fish_mkdir_p --tree $_dir
         touch $_path
     end
 end