Add .gitattributes: force LF line-endings for deterministic baseline

Without .gitattributes the checkout line-endings depend on the build
host's core.autocrlf. On the tanis host this produced CRLF: build-baseline.sh
died with `bash\r`, and a CRLF build tree would break the baseline-diff
byte-match. Pin `* text=auto eol=lf` so the source-of-truth LF is
authoritative regardless of client config; binary assets stay byte-exact.

Assisted-by: claude-code@claude-opus-4-8

.gitattributes

@@ -0,0 +1,21 @@
+# Determinisztikus sorvég (illusion3-salt#895 CRLF-incidens): a baseline
+# byte-pontossága a source-of-truth LF-jén múlik, NEM a build-kliens
+# core.autocrlf-jén. A build-baseline.sh shebangja CRLF esetén 'bash\r'-t
+# keresett és eltört; a build out/ CRLF-je pedig a baseline-diffet rontja.
+* text=auto eol=lf
+# bináris assetek — a git ne konvertáljon, byte-pontos marad
+*.png binary
+*.jpg binary
+*.jpeg binary
+*.gif binary
+*.ico binary
+*.webp binary
+*.woff binary
+*.woff2 binary
+*.ttf binary
+*.eot binary
+*.otf binary
+*.zip binary
+*.gz binary
+*.pdf binary
+*.swf binary