Delete install/ on workspace path change to fix stale binaries

Updating .pc and .cmake config files with sed is insufficient — the MFC
executables (simulation, pre_process, post_process) and static libraries
have the old runner workspace path baked in at compile time. When the
cache moves between runner instances, these binaries fail at runtime.

Replace the install/ sed fix with rm -rf install/ so CMake re-links and
re-installs all binaries with correct paths. The staging/ object files
remain valid, so this is a re-link, not a full rebuild.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sbryngelson

.github/scripts/setup-build-cache.sh

@@ -82,10 +82,10 @@ if [ -f "$_workspace_marker" ]; then
                -o -name "*.make" -o -name "Makefile" \
                -o -name "build.ninja" \) \
             -exec sed -i "s|${_old_workspace}|$(pwd)|g" {} + 2>/dev/null || true
-        # Update pkg-config and cmake config files in install/
-        find "$_cache_dir/install" -type f \
-            \( -name "*.pc" -o -name "*.cmake" \) \
-            -exec sed -i "s|${_old_workspace}|$(pwd)|g" {} + 2>/dev/null || true
+        # Compiled binaries have stale paths baked in — delete install/
+        # so CMake rebuilds and re-installs them with correct paths.
+        echo "  Clearing install/ to force rebuild of binaries..."
+        rm -rf "$_cache_dir/install"
     fi
 fi
 echo "$(pwd)" > "$_workspace_marker"