feat: rename app to Last Signal

Rename service, UI, storage, and target-path configuration; clarify expiration cleanup behavior.

scripts/cleanup.sh

@@ -1,20 +1,35 @@
 #!/bin/sh
 set -eu
 
-TARGET="${COLLECTION_PATH:-/home/zenn/Collection}"
+TARGET="${TARGET_PATH:-/home/zenn/Collection}"
 
 case "$TARGET" in
-  /home/zenn/Collection) ;;
+  /*) ;;
   *)
-    echo "[collection-keeper] refused unsafe path: $TARGET"
+    echo "[last-signal] refused non-absolute target path: $TARGET"
     exit 1
     ;;
 esac
 
-if [ ! -e "$TARGET" ]; then
-  echo "[collection-keeper] target not found: $TARGET"
+if [ -L "$TARGET" ]; then
+  echo "[last-signal] refused symbolic-link target: $TARGET"
+  exit 1
+fi
+
+if [ ! -d "$TARGET" ]; then
+  if [ -e "$TARGET" ]; then
+    echo "[last-signal] refused non-directory target: $TARGET"
+    exit 1
+  fi
+  echo "[last-signal] target directory not found: $TARGET"
   exit 0
 fi
 
-rm -rf -- "$TARGET"
-echo "[collection-keeper] deleted: $TARGET"
+TARGET_REAL="$(CDPATH= cd "$TARGET" && pwd -P)"
+if [ "$TARGET_REAL" = "/" ]; then
+  echo "[last-signal] refused filesystem root"
+  exit 1
+fi
+
+find "$TARGET_REAL" -mindepth 1 -maxdepth 1 -exec rm -rf -- {} +
+echo "[last-signal] deleted contents of: $TARGET_REAL"