chore(ci): ignore generated requirements exports in jscpd

requirements/*.txt are hash-pinned exports written by `just lock` and
checked byte-for-byte by scripts/check_exports.py. Duplication between
them is the lock's output, not hand-written code, so it is excluded
from the duplication gate. The threshold and minLines/minTokens are
unchanged.

.jscpd.json

@@ -13,6 +13,7 @@
     "**/dist/**",
     "**/build/**",
     "**/*.lock",
+    "requirements/*.txt",
     "**/package-lock.json",
     "**/*.md",
     "docs/**"