C1: shower — copy wheel to clean filename before pip install

Nix store paths embed a 32-char hash prefix, which pip rejects as
"Invalid wheel filename (invalid version)". Copy the wheel into TMPDIR
under its bare name first, then install from there.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

containers/shower/default.nix

@@ -82,10 +82,16 @@ let
 
       ${python}/bin/python -m venv "$TMPDIR/venv"
       "$TMPDIR/venv/bin/pip" install --upgrade pip
+
+      # Nix store paths embed a 32-char hash prefix, which pip's wheel
+      # filename parser rejects ("Invalid wheel filename"). Copy to a
+      # clean filename in TMPDIR before installing.
+      cp ${showerWheel} "$TMPDIR/${showerWheel.name}"
+
       "$TMPDIR/venv/bin/pip" install \
         --no-cache-dir \
         --index-url=https://pypi.ops.eblu.me/root/pypi/+simple/ \
-        ${showerWheel} \
+        "$TMPDIR/${showerWheel.name}" \
         gunicorn
 
       runHook postBuild