Add line-ending policy to .gitattributes; renormalize

* text=auto eol=lf (store LF, check out LF) with *.ps1 text eol=crlf so the
Windows PowerShell scripts stay CRLF. Prevents the CRLF<->LF churn that made the
whole-file diffs. The .ps1 working-tree bytes are unchanged.

.gitattributes

@@ -4,3 +4,9 @@
 *.txt linguist-detectable=false
 *.json linguist-detectable=false
 *.ps1 linguist-detectable=false
+
+# Line endings: store LF in the repository; check out LF everywhere except the
+# Windows PowerShell scripts, which stay CRLF. Prevents CRLF<->LF churn.
+* text=auto eol=lf
+*.ps1 text eol=crlf
+