fix: preserve LF line endings for shell checkouts

[Kewe63]

Summary

Fixes #73.

The repository's shell-script blobs already contain LF line endings. The failure occurs during checkout: with core.autocrlf=true, Git converts them to CRLF because the repository has no explicit shell-file EOL policy. Linux then cannot resolve the CR-terminated shebang interpreter; explicitly invoking a shell also fails on the CR-terminated shell statements.

• Add *.sh text eol=lf to preserve LF in shell-script checkouts, including progress.sh and scripts mounted as Linux container entrypoints.
• Add regression tests using the real repository shell files and actual Git index/checkout conversion in disposable repositories.
• Do not rewrite already-LF scripts, change global Git settings, or normalize unrelated file types.

Verification

• Before the rule: the regression's core.autocrlf=true case failed for all five scripts; false and input controls passed.
• After the rule: python3 -m unittest discover -s tests -v passes all three cases with Git 2.43.0 on Linux.
• GIT_BINARY='/mnt/c/Program Files/Git/cmd/git.exe' python3 -m unittest discover -s tests -v also passes all three cases with actual Git for Windows 2.52.0.windows.1, invoked from WSL.
• Each case checks all five current shell scripts against the original bytes and rejects CRLF after checkout.
• The fixture removes only its own temporary worktree copies before checkout-index so Git actually rematerializes the files rather than taking a stat-cache shortcut.
• git diff --cached --check passes.

The preceding issue investigation separately reproduced failures by executing the actual CRLF checkouts in an isolated Linux environment: direct invocation returned 127 (missing CR-suffixed interpreter), explicit shell invocation returned 2, and LF controls succeeded. No Docker, live RPC, or existing node data was used.

Scope and limitations

This is a checkout policy fix, not a claim that the committed scripts contain CRLF or that every Windows setup is affected. Windows Git was tested through WSL using UNC paths; Docker Desktop end-to-end startup was not run.

The rule governs future checkout materialization. Adding it does not itself rewrite pre-existing CRLF working files: operators must preserve local edits and refresh affected files or use a fresh checkout after updating. No destructive refresh command or global configuration change is included.

This change is independent of the WebSocket fix in #91 and uses a separate test module. PR #83 concerns .env parsing, not shell-file checkout conversion.

Implementation and test preparation were AI-assisted.