Fix commands failing when current directory path contains spaces

[Copilot]

Commands were failing with "too many arguments" error when the current working directory's full path contained spaces. This happened because the run method in Commands was using simple string joining instead of proper shell escaping.

The issue occurred in this line:

stdout = `#{cmd.join(" ")}`.chomp

When a path like /home/my work/repo was part of the command arguments, the shell would incorrectly parse it as multiple separate arguments instead of a single path.

Before fix:

cmd = ["/home/my work/repo/exe/litestream", "databases", "--config", "/home/my work/repo/config/litestream.yml"]
cmd.join(" ")
# => "/home/my work/repo/exe/litestream databases --config /home/my work/repo/config/litestream.yml"
# Shell sees 6 arguments: ["/home/my", "work/repo/exe/litestream", "databases", "--config", "/home/my", "work/repo/config/litestream.yml"]
# Result: ERROR failed to run error="too many arguments"

After fix:

Shellwords.shelljoin(cmd)
# => "/home/my\\ work/repo/exe/litestream databases --config /home/my\\ work/repo/config/litestream.yml"  
# Shell correctly sees 4 arguments: ["/home/my work/repo/exe/litestream", "databases", "--config", "/home/my work/repo/config/litestream.yml"]
# Result: Commands work correctly

The fix uses Shellwords.shelljoin(cmd) which properly escapes spaces and other shell metacharacters, ensuring arguments are parsed correctly regardless of their content.

Fixes #66.

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