copy: ** glob patterns don't match root-level files on macOS (Bash 3.2 find fallback)

[okazuki58]

Description

When using ** glob patterns in gtr.copy.include config, root-level files are not copied on macOS (which uses Bash 3.2 by default).

Steps to Reproduce

1. macOS with default Bash 3.2
2. .gtrconfig:

   [copy]
   include = **/.env*
   include = **/CLAUDE.md

3. Root-level .env and CLAUDE.md exist in the main repo
4. Run git gtr copy <worktree-name>

Expected

Root-level .env and CLAUDE.md are copied to the worktree.

Actual

==> Copying to: <branch-name>
[!] Failed to copy
[!] Failed to copy

With --dry-run:

==> [dry-run] Would copy to: <branch-name>
[OK] [dry-run] Would copy: 
[OK] [dry-run] Would copy: 
[OK] [dry-run] Would copy 2 file(s)

File names are empty in the output.

Root Cause

In lib/copy.sh, when Bash 3.2 doesn't support globstar, the code falls back to find:

$(find . -path "./$pattern" -type f 2>/dev/null)

For pattern **/.env*, this becomes find . -path "./**/.env*" -type f.

The problem is twofold:

1. find -path doesn't treat ** as recursive glob — it's just a regular wildcard. The pattern **/.env* requires a directory separator before .env, so it never matches root-level files like ./.env.

2. Empty results still trigger one loop iteration — when find returns nothing, the while read loop with heredoc executes once with an empty string, causing cp "" <dest> to fail.

Workaround

Use patterns without **/ prefix:

[copy]
include = .env*
include = CLAUDE.md

Suggested Fix

1. For **-prefixed patterns, also match root-level files (e.g., convert **/.env* to find . -name ".env*" -type f)
2. Add an empty-string guard in the copy loop: [ -z "$file" ] && continue