fix: accumulate message words instead of overwriting in cmd_continue

The for loop was overwriting message each iteration, causing only
the last word to survive. Changed to accumulate all words with
proper spacing.

Fixes #225

skills/kugetsu/scripts/kugetsu-session.sh

@@ -379,10 +379,9 @@ cmd_start() {
     
     cd "$worktree_path"
     local sanitized_id=$(echo "$new_session_id" | sed 's/[^a-zA-Z0-9_-]/_/g')
-    local msg_file="$LOGS_DIR/msg-$sanitized_id.txt"
+    local msg_file="$worktree_path/.kugetsu-msg.txt"
     printf '%s' "$dev_message" > "$msg_file"
     nohup sh -c "GITEA_TOKEN='${GITEA_TOKEN:-}' opencode run '@$msg_file' --session '$new_session_id'" >> "$LOGS_DIR/dev-$sanitized_id.log" 2>&1 &
-    rm -f "$msg_file"
     
     echo "Session started for '$issue_ref': $new_session_id"
     echo "Worktree: $worktree_path"
@@ -399,7 +398,7 @@ cmd_continue() {
         if [ -z "$session_name" ]; then
             session_name="$arg"
         else
-            message="$arg"
+            message="${message}${message:+ }${arg}"
         fi
     done
     
@@ -446,10 +445,9 @@ cmd_continue() {
     
     cd "$worktree_path"
     local sanitized_id=$(echo "$opencode_session_id" | sed 's/[^a-zA-Z0-9_-]/_/g')
-    local msg_file="$LOGS_DIR/msg-$sanitized_id.txt"
+    local msg_file="$worktree_path/.kugetsu-msg.txt"
     printf '%s' "$message" > "$msg_file"
     nohup sh -c "GITEA_TOKEN='${GITEA_TOKEN:-}' opencode run '@$msg_file' --session '$opencode_session_id'" >> "$LOGS_DIR/dev-$sanitized_id.log" 2>&1 &
-    rm -f "$msg_file"
 }
 
 cmd_list() {