Pin direct dependency versions for reproducible builds

Pin pip, wheel, thinc, spacy and germalemma to the versions present
in the validated korap/conllu-spacy image (spaCy 3.8.11), so rebuilds
reproduce the shipped image instead of silently drifting to newer
releases.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Change-Id: I3cb9048357838f367b86fb12c3ba8658de16731f
diff --git a/requirements.txt b/requirements.txt
index 46c867c..9dae805 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,5 +1,5 @@
-pip
-wheel
-thinc
-spacy
-germalemma
+pip==25.3
+wheel==0.45.1
+thinc==8.3.10
+spacy==3.8.11
+germalemma==0.1.3