fix: use ${GITEA_TOKEN:-} to handle unset token

With set -u, expanding $GITEA_TOKEN fails if not set.
Changed to ${GITEA_TOKEN:-} to provide empty default.
This fixes the issue where cmd_start appears to succeed but agent never runs.

skills/kugetsu/scripts/kugetsu-session.sh

@@ -195,7 +195,7 @@ cmd_delegate() {
     mkdir -p "$LOGS_DIR"
     local log_file="$LOGS_DIR/delegate-$(date +%s).log"
     load_agent_env "pm-agent"
-    nohup sh -c "GITEA_TOKEN='$GITEA_TOKEN' opencode run '$message' --continue --session '$pm_session'" >> "$log_file" 2>&1 &
+    nohup sh -c "GITEA_TOKEN='${GITEA_TOKEN:-}' opencode run '$message' --continue --session '$pm_session'" >> "$log_file" 2>&1 &
     echo "Delegated to PM agent (logged to $(basename "$log_file"))"
 }
 
@@ -314,7 +314,7 @@ cmd_start() {
     load_agent_env "dev"
     
     cd "$worktree_path"
-    nohup sh -c "GITEA_TOKEN='$GITEA_TOKEN' opencode run '$dev_message' --continue --session '$new_session_id'" >> "$LOGS_DIR/dev-$new_session_id.log" 2>&1 &
+    nohup sh -c "GITEA_TOKEN='${GITEA_TOKEN:-}' opencode run '$dev_message' --continue --session '$new_session_id'" >> "$LOGS_DIR/dev-$new_session_id.log" 2>&1 &
     
     echo "Session started for '$issue_ref': $new_session_id"
     echo "Worktree: $worktree_path"
@@ -369,9 +369,9 @@ cmd_continue() {
     
     if [ -n "$worktree_path" ] && [ -d "$worktree_path" ]; then
         cd "$worktree_path"
-        nohup sh -c "GITEA_TOKEN='$GITEA_TOKEN' opencode run '$message' --continue --session '$opencode_session_id'" >> "$LOGS_DIR/dev-$opencode_session_id.log" 2>&1 &
+        nohup sh -c "GITEA_TOKEN='${GITEA_TOKEN:-}' opencode run '$message' --continue --session '$opencode_session_id'" >> "$LOGS_DIR/dev-$opencode_session_id.log" 2>&1 &
     else
-        nohup sh -c "GITEA_TOKEN='$GITEA_TOKEN' opencode run '$message' --continue --session '$opencode_session_id'" >> "$LOGS_DIR/dev-$opencode_session_id.log" 2>&1 &
+        nohup sh -c "GITEA_TOKEN='${GITEA_TOKEN:-}' opencode run '$message' --continue --session '$opencode_session_id'" >> "$LOGS_DIR/dev-$opencode_session_id.log" 2>&1 &
     fi
 }
 
@@ -523,7 +523,7 @@ cmd_destroy() {
     local target="${1:-}"
     local force=false
     
-    if [ "$2" = "-y" ]; then
+    if [ "${2:-}" = "-y" ]; then
         force=true
     fi