fix(compile): pin LF eol on managed gitattributes entries

[Copilot]

On Windows (default core.autocrlf=true), every recompile produced warning: in the working copy of '<pipeline>.yml', LF will be replaced by CRLF the next time Git touches it, because the compiler writes LF but Git assumed CRLF was canonical for these files.

Summary

• src/compile/gitattributes.rs: extend the per-file ATTRIBUTES constant from linguist-generated=true merge=ours to linguist-generated=true merge=ours text eol=lf, declaring LF as the canonical EOL for compiled pipelines.
• Writer behavior is unchanged — files are still emitted as LF, so working-copy bytes stay stable across platforms and ado-aw check integrity holds.
• No repo-level .gitattributes change: the managed block already enumerates every compiled pipeline.

Resulting line per pipeline:

agents/foo.lock.yml linguist-generated=true merge=ours text eol=lf

Test plan

• Updated substring assertions in the four affected tests (writes_new_gitattributes_when_missing, preserves_user_managed_lines, replaces_existing_managed_block, quotes_paths_containing_spaces).
• Added entries_pin_lf_eol regression test so the text eol=lf attribute can't be silently dropped.
• cargo test and cargo clippy --all-targets --all-features both clean.