SW-21: Pin shell scripts to LF via .gitattributes

[developzoneio]

Summary

Adds a repo-root .gitattributes so shell scripts stop checking out as CRLF on Windows. With
core.autocrlf=true (Git's default on Windows and on the windows-latest CI runner) the repo had
no .gitattributes, so every tracked *.sh / *.ps1 was stored LF in the index but checked out
CRLF. A #!/usr/bin/env bash line with a trailing CR makes the kernel look for interpreter bash\r
(bad interpreter error); heredocs and [[ ... ]] comparisons also mis-parse on a trailing CR.

Policy applied: * text=auto default, plus *.sh and *.ps1 pinned to text eol=lf.

⚠️ One-time renormalization

The first checkout after this lands rewrites line endings in existing Windows working trees. It
looks like a large diff but is a one-time renormalization, not a content change. The index was
already all-LF, so git add --renormalize produced no content churn.

Notes (ticket premise was stale)

The ticket assumed SW-18 had added a narrow tests/lessons/** rule to fold in. Verified false: no
SW-18 commit, no tests/lessons/ directory, no scripts/selftest-docs.*. So this creates a fresh
file rather than folding an existing rule. Also, exposure is broader than the ticket stated: CI's
windows-latest runner already runs bash scripts/*.sh on a CRLF checkout, passing only because
Git Bash tolerates the CR today - this hardens that fragile path.

Verification

• Fresh clone: git ls-files --eol reports w/lf + attr/text eol=lf for all 14 scripts; 0 CR
  bytes across all .sh; shebang ends bash \n.
• bash -n parses every shell script.
• scripts/validate.sh -> [OK] All checks passed; ASCII rule clean on all *.ps1.
• scripts/smoke-hooks.sh local failures are pre-existing/environmental (jq absent locally;
  identical on the pre-change baseline). Green on CI where jq is present.

Closes SW-21.

🤖 Generated with Claude Code

[developzoneio]

Superseded: the SW-21 .gitattributes fix was merged into feature/optimize-workflow/v1 (commit 8a8e0be), which folds it together with the existing narrow tests/** fixture pins. Closing this standalone PR to avoid a duplicate merge into main.