build: add .gitattributes to enforce LF line endings

Forces all text files to use LF on commit regardless of the editor or
OS that wrote them. Prevents the line-ending churn that has been
inflating diffs (e.g. 1510 lines of churn on config.py in commit
493b43f for what was really a 12-line change). The next commit will
normalize all existing files; from there forward, diffs only show
real semantic changes.

.gitattributes

@@ -0,0 +1,25 @@
+# Enforce LF line endings on commit for all text files
+* text=auto eol=lf
+
+# Explicit overrides for files that must keep specific endings
+*.bat       text eol=crlf
+*.cmd       text eol=crlf
+*.ps1       text eol=crlf
+
+# Binary files — never touch
+*.png       binary
+*.jpg       binary
+*.jpeg      binary
+*.gif       binary
+*.ico       binary
+*.pdf       binary
+*.db        binary
+*.sqlite    binary
+*.sqlite3   binary
+*.zip       binary
+*.tar       binary
+*.gz        binary
+*.woff      binary
+*.woff2     binary
+*.ttf       binary
+*.eot       binary