chore: pin line endings to LF

Line endings were left to whatever core.autocrlf each machine happens to be
configured with. On a second machine that alone is enough to present every
tracked file as modified, burying real changes in noise. The index already
holds LF, so nothing needs renormalizing.

Claude-Session: https://claude.ai/code/session_0158owAAsXAfFiT3hGkQt1Xk

.gitattributes

@@ -0,0 +1,4 @@
+# Zeilenenden im Repository immer LF, unabhaengig von core.autocrlf des
+# jeweiligen Rechners. Ohne das erzeugt ein Wechsel zwischen Windows und
+# einem anderen System Diffs, die nur aus Zeilenenden bestehen.
+* text=auto eol=lf