Improve install log handling for containers

Enhances the build and error handler scripts to better manage installation logs. On install failure, the log is now copied from the container to the host for easier debugging. The error handler now saves the log inside the container's /root directory for later retrieval, improving traceability and support.

misc/build.func

@@ -2518,7 +2518,12 @@ EOF'
 
   # Run application installer
   if ! lxc-attach -n "$CTID" -- bash -c "$(curl -fsSL https://raw.githubusercontent.com/community-scripts/ProxmoxVED/main/install/${var_install}.sh)"; then
-    exit $?
+    local exit_code=$?
+    # Try to copy installation log from container before exiting
+    if [[ -n "$CTID" && -n "${SESSION_ID:-}" ]]; then
+      pct pull "$CTID" "/root/.install-${SESSION_ID}.log" "/tmp/install-${SESSION_ID}.log" 2>/dev/null || true
+    fi
+    exit $exit_code
   fi
 }