chore: add .gitattributes enforcing LF

The repo had none, and core.autocrlf=true is the usual Git-on-Windows
setting, so a clone, checkout, or stash pop silently rewrites every text file
to CRLF. That fails format:check against prettier's endOfLine: lf - it
already turned the gate red once mid-branch, after a stash round-trip
reintroduced CRLF into files that had been committed clean.

Verified: no tracked file currently carries a CR byte at HEAD.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.gitattributes

@@ -0,0 +1,16 @@
+# Enforce LF in the working tree regardless of a contributor's core.autocrlf.
+# Without this, Git on Windows smudges every text file to CRLF on clone, stash
+# pop, or checkout, which fails `bun run format:check` (prettier endOfLine: lf).
+* text=auto eol=lf
+
+# Binary assets Git must not touch.
+*.png binary
+*.jpg binary
+*.jpeg binary
+*.gif binary
+*.webp binary
+*.ico binary
+*.pdf binary
+*.woff binary
+*.woff2 binary
+*.db binary