feat(session): integrate kugetsu_context_dump into delegation flow

- Call kugetsu_context_dump() in cmd_start() before forking agent
- Call kugetsu_context_dump() in cmd_continue() before forking agent
- Captures initial user prompt in context JSON for session resumption

Closes #212

skills/kugetsu/scripts/kugetsu-session.sh

@@ -405,6 +405,8 @@ cmd_start() {
     
     local dev_message=$(build_dev_agent_message "$issue_ref" "$message")
     
+    kugetsu_context_dump "$issue_ref" "$dev_message" "$(issue_ref_to_branch_name "$issue_ref")"
+    
     load_agent_env "dev"
     
     cd "$worktree_path"
@@ -477,6 +479,8 @@ cmd_continue() {
         message=$(build_dev_agent_message "$issue_ref" "")
     fi
     
+    kugetsu_context_dump "$issue_ref" "$message" "$(issue_ref_to_branch_name "$issue_ref")"
+    
     cd "$worktree_path"
     local sanitized_id=$(echo "$opencode_session_id" | sed 's/[^a-zA-Z0-9_-]/_/g')
     mkdir -p "$worktree_path/.kugetsu"