[FIX] Add .gitattributes so POSIX scripts stay LF on Windows clones

[pranayr710]

Fixes #2345

Reason for this PR:

• This PR fixes a bug that I have personally experienced (it broke my own Docker build) and which reproduces from a clean clone in three commands.

Sanity check:

• I have read and understood the contributors guide.
• I have checked that another pull request for this purpose does not exist.
• Bug fix, so NOT added to the changelog.
• Not adding new C code.

---

What was wrong

There is no .gitattributes in the tree. Git for Windows defaults to core.autocrlf=true, so a clone made on Windows gets CRLF in every text file — including the shebang of all 16 POSIX shell scripts. docker/Dockerfile runs RUN ./pre-build.sh, and that fails:

/usr/bin/env: 'bash\r': No such file or directory
ERROR: process "/bin/sh -c ./pre-build.sh" did not complete successfully: exit code: 127

CONTRIBUTING.md asks for "Unix line endings" but nothing enforces it.

Before / after

Clone with Git's default Windows setting, then run the project's own pre-build step under Linux:

clone of	linux/pre-build.sh	./pre-build.sh
master	CRLF line terminators	exit 127
this branch	LF	exit 0

# before
git -c core.autocrlf=true clone --depth 1 https://github.com/CCExtractor/ccextractor.git
docker run --rm -v $PWD/ccextractor:/src -w /src/linux debian:bookworm-slim \
    sh -c './pre-build.sh; echo exit=$?'
#   /usr/bin/env: 'bash\r': No such file or directory
#   exit=127

Scope

Deliberately narrow — no * text=auto. 978 tracked files are currently committed with CRLF (Visual Studio project files and similar), so a blanket rule would renormalise the whole repo and bury this fix in noise. The rules here name only POSIX scripts (eol=lf) and Windows scripts (eol=crlf).

I verified with git add --renormalize . that adding this file changes no tracked file's content: the commit is the new file and nothing else.

The *.bat / *.ps1 lines are the mirror case and are a no-op today (those files are already CRLF); they are there so the inverse problem cannot appear later. Happy to drop them if you'd rather keep the file to the LF half.