feat(init): add interactive fzf worktree picker for gtr cd

When `gtr cd` is called with no arguments and fzf is installed, an
interactive picker launches showing all worktrees with a git log + status
preview pane. Gracefully falls back to printing the worktree list with a
hint when fzf is not available. Supported in bash, zsh, and fish shells.

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

Author: karan925

README.md

@@ -100,6 +100,7 @@ git gtr ai my-feature           # Start claude
 git gtr run my-feature npm test # Run tests
 
 # Navigate to worktree
+gtr cd                          # Interactive picker (requires fzf + shell integration)
 gtr cd my-feature               # Requires: eval "$(git gtr init bash)"
 cd "$(git gtr go my-feature)"   # Alternative without shell integration
 
@@ -217,6 +218,7 @@ cd "$(git gtr go 1)"             # Navigate to main repo
 eval "$(git gtr init bash)"
 
 # Then navigate with:
+gtr cd                # Interactive worktree picker (requires fzf)
 gtr cd my-feature
 gtr cd 1
 ```

lib/commands/doctor.sh

@@ -112,6 +112,13 @@ cmd_doctor() {
     fi
   fi
 
+  # Check fzf (optional, for interactive picker)
+  if command -v fzf >/dev/null 2>&1; then
+    echo "[OK] fzf: $(fzf --version 2>/dev/null | awk '{print $1}') (interactive picker available)"
+  else
+    echo "[i] fzf: not found (install for interactive picker: gtr cd)"
+  fi
+
   echo ""
   if [ "$issues" -eq 0 ]; then
     echo "Everything looks good!"

lib/commands/help.sh

@@ -365,6 +365,7 @@ Setup:
   eval "$(git gtr init zsh --as gwtr)"
 
 After setup:
+  gtr cd                                        # interactive worktree picker (requires fzf)
   gtr cd my-feature                             # cd to worktree
   gtr cd 1                                      # cd to main repo
   gtr <command>                                 # same as git gtr <command>
@@ -549,6 +550,7 @@ SETUP & MAINTENANCE:
          Generate shell integration for cd support (bash, zsh, fish)
          --as <name>: custom function name (default: gtr)
          Usage: eval "$(git gtr init bash)"
+         With fzf installed, 'gtr cd' (no args) opens an interactive picker
 
   version
          Show version
@@ -572,6 +574,7 @@ WORKFLOW EXAMPLES:
   git gtr run feature/user-auth npm run dev   # Start dev server
 
   # Navigate to worktree directory
+  gtr cd                                    # Interactive picker (requires fzf)
   gtr cd feature/user-auth                  # With shell integration (git gtr init)
   cd "$(git gtr go feature/user-auth)"      # Without shell integration
 

lib/commands/init.sh

@@ -81,6 +81,23 @@ _init_bash() {
 __FUNC__() {
   if [ "$#" -gt 0 ] && [ "$1" = "cd" ]; then
     shift
+    if [ "$#" -eq 0 ]; then
+      if command -v fzf >/dev/null 2>&1; then
+        local _gtr_sel
+        _gtr_sel="$(command git gtr list --porcelain | fzf \
+          --delimiter=$'\t' \
+          --with-nth=2 \
+          --header='Select worktree (Ctrl-C to cancel)' \
+          --preview='git -C {1} log --oneline --graph -15 2>/dev/null; echo "---"; git -C {1} status --short 2>/dev/null' \
+          --preview-window=right:50%)" || return 0
+        set -- "$(printf '%s' "$_gtr_sel" | cut -f2)"
+      else
+        echo "Tip: Install fzf for an interactive worktree picker (https://github.com/junegunn/fzf)" >&2
+        echo "" >&2
+        command git gtr list
+        return 0
+      fi
+    fi
     local dir
     dir="$(command git gtr go "$@")" && cd "$dir" && {
       local _gtr_hooks _gtr_hook _gtr_seen _gtr_config_file
@@ -154,6 +171,23 @@ _init_zsh() {
 __FUNC__() {
   if [ "$#" -gt 0 ] && [ "$1" = "cd" ]; then
     shift
+    if [ "$#" -eq 0 ]; then
+      if command -v fzf >/dev/null 2>&1; then
+        local _gtr_sel
+        _gtr_sel="$(command git gtr list --porcelain | fzf \
+          --delimiter=$'\t' \
+          --with-nth=2 \
+          --header='Select worktree (Ctrl-C to cancel)' \
+          --preview='git -C {1} log --oneline --graph -15 2>/dev/null; echo "---"; git -C {1} status --short 2>/dev/null' \
+          --preview-window=right:50%)" || return 0
+        set -- "$(printf '%s' "$_gtr_sel" | cut -f2)"
+      else
+        echo "Tip: Install fzf for an interactive worktree picker (https://github.com/junegunn/fzf)" >&2
+        echo "" >&2
+        command git gtr list
+        return 0
+      fi
+    fi
     local dir
     dir="$(command git gtr go "$@")" && cd "$dir" && {
       local _gtr_hooks _gtr_hook _gtr_seen _gtr_config_file
@@ -232,7 +266,25 @@ _init_fish() {
 
 function __FUNC__
   if test (count $argv) -gt 0; and test "$argv[1]" = "cd"
-    set -l dir (command git gtr go $argv[2..])
+    set -l _gtr_cd_args $argv[2..]
+    if test (count $_gtr_cd_args) -eq 0
+      if command -q fzf
+        set -l _gtr_sel (command git gtr list --porcelain | fzf \
+          --delimiter=\t \
+          --with-nth=2 \
+          --header='Select worktree (Ctrl-C to cancel)' \
+          --preview='git -C {1} log --oneline --graph -15 2>/dev/null; echo "---"; git -C {1} status --short 2>/dev/null' \
+          --preview-window=right:50%)
+        or return 0
+        set _gtr_cd_args (printf '%s' "$_gtr_sel" | cut -f2)
+      else
+        echo "Tip: Install fzf for an interactive worktree picker (https://github.com/junegunn/fzf)" >&2
+        echo "" >&2
+        command git gtr list
+        return 0
+      end
+    end
+    set -l dir (command git gtr go $_gtr_cd_args)
     and cd $dir
     and begin
       set -l _gtr_hooks