cfg_default doesn't read from .gtrconfig (missing file_key auto-mapping)

[pkohei]

Summary

The cfg_default function doesn't read settings from .gtrconfig because it lacks the auto-mapping feature that cfg_get_all has. This affects gtr.worktrees.dir and gtr.defaultBranch settings.

Steps to Reproduce

1. Create a .gtrconfig file:

[worktrees]
    dir = /worktrees

2. Run git gtr new test

3. Expected: Worktree created in /worktrees/test

4. Actual: Worktree created in default location (<repo>-worktrees/test)

Root Cause

In lib/config.sh, cfg_get_all has auto-mapping (lines 115-117):

# Auto-map file_key if not provided and key is a gtr.* key
if [ -z "$file_key" ] && [[ "$key" == gtr.* ]]; then
  file_key=$(cfg_map_to_file_key "$key")
fi

But cfg_default doesn't have this, so when called without file_key:

# lib/core.sh line 51
base_dir=$(cfg_default "gtr.worktrees.dir" "GTR_WORKTREES_DIR" "")

The .gtrconfig is never checked.

Suggested Fix

Add auto-mapping to cfg_default:

cfg_default() {
  local key="$1"
  local env_name="$2"
  local fallback="$3"
  local file_key="${4:-}"

  # Auto-map file_key if not provided and key is a gtr.* key
  if [ -z "$file_key" ] && [[ "$key" == gtr.* ]]; then
    file_key=$(cfg_map_to_file_key "$key")
  fi
  # ... rest of function

Workaround

Use git config --local instead:

git config --local gtr.worktrees.dir /worktrees

[helizaga]

addressed here:
#88