feat(fzf): add preview, dirs, and image support to @@ inline picker

The @@ picker only listed files with no preview. It now lists both
files and directories via fd (matching _fzf_search_directory), and
shows a bat-highlighted or image-rendered preview through
_fzf_preview_file. Image previews use a kitty-graphics-protocol,
chafa, viu, timg fallback chain via the new _fzf_preview_image
helper, benefiting the Ctrl+F directory search and git-status
pickers as well since they share the same preview helper.

functions/__fzf_inline_picker.fish

@@ -7,9 +7,12 @@
 # DESCRIPTION
 #   Bound to the @ key. Self-inserts @ normally; on a second consecutive @
 #   (detected by looking behind at the current token rather than making fish
-#   buffer ahead for a chord), opens an interactive fzf session and replaces
-#   the bare @ with the selected item. Cancelling leaves a literal @@ behind.
-#   Repaints the prompt after selection or cancellation.
+#   buffer ahead for a chord), opens an interactive fzf session listing both
+#   files and directories under the current directory, with a preview pane
+#   (bat-highlighted for text, image-rendered for pictures via
+#   _fzf_preview_file), and replaces the bare @ with the selected item.
+#   Cancelling leaves a literal @@ behind. Repaints the prompt after
+#   selection or cancellation.
 #
 # EXIT STATUS
 #   0  Always
@@ -20,7 +23,22 @@
 #   # (e.g. a trailing /subdir).
 function __fzf_inline_picker
     if test (commandline -t) = @
-        set -l selection (fzf)
+        # Directly use fd binary to avoid output buffering delay caused by a fd
+        # alias, if any. Debian-based distros install fd as fdfind.
+        set -f fd_cmd (command -v fdfind || command -v fd || echo "fd")
+        set -f --append fd_cmd --color=always $fzf_fd_opts
+
+        set -l selection ($fd_cmd 2>/dev/null | _fzf_wrapper --ansi \
+            --height=90% \
+            --layout=reverse \
+            --border=rounded \
+            --border-label=' Insert Path ' \
+            --prompt='@@ -> ' \
+            --header='Enter: Insert  Ctrl-/: Toggle Preview  Esc: Cancel' \
+            --bind='ctrl-/:toggle-preview' \
+            --preview='_fzf_preview_file {}' \
+            --preview-window='right:50%:wrap:border-left')
+
         if test -n "$selection"
             commandline -t -- (string escape -- $selection)
         else