fix(ci): use if-statements in stage(), not bare [ -f ] && cp, for set -e safety

GitHub Actions runs each `run:` step under `bash -e`. A top-level
`[ -f "$1" ] && cp ...` line is NOT exempt from -e the way an if-condition
is: when the test is false, the line's exit status is 1 and the whole step
aborts immediately — which is exactly what happened on the very first
stage() call, since pdfium/encoder/bbox have no .data sidecar to copy.
Rewriting as explicit if/fi blocks (which set -e does exempt) fixes it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DofkqhMuAJbL9arnnuVisL

Author: claude

.github/workflows/publish-models.yml

@@ -90,8 +90,8 @@ jobs:
         run: |
           mkdir -p release-assets
           stage() { # <source-path> <asset-name>
-            [ -f "$1" ] && cp "$1" "release-assets/$2"
-            [ -f "$1.data" ] && cp "$1.data" "release-assets/$2.data"
+            if [ -f "$1" ]; then cp "$1" "release-assets/$2"; fi
+            if [ -f "$1.data" ]; then cp "$1.data" "release-assets/$2.data"; fi
           }
           stage third-party/lib/libpdfium.so libpdfium.so
           stage third-party/ocr_rec.onnx ocr_rec.onnx