batwatch: Show 'Command:' instead of 'File:' in header of command mode

[frankenstein91]

Description

When running batwatch --command <cmd>, the header rendered by bat displays File: <cmd>. Since it is executing a command rather than displaying a file, it is more appropriate and intuitive to display Command: <cmd>.

This PR post-processes the bat output in batwatch's command execution loop using a portable sed replacement that targets only the first 5 lines (the header block), changing File: to Command:.

Changes

• src/batwatch.sh: Added a portable Basic Regular Expression (BRE) sed filter in the output capturing pipeline to replace the File: label with Command:.
• test/suite/batwatch.sh: Added the test:command_header test case to verify that the header correctly uses Command: when executing a command.

Verification

Tested both the raw script and the compiled version using the test suite:

• ./test.sh (all batwatch tests pass)
• ./build.sh && ./test.sh --compiled (all batwatch tests pass)