Switch the session project context directory for Harmony project actions.

Use this tool before running `build_project` or `start_app`.
These tools only work correctly when the context directory is a valid project path.
If the current context directory is already the ArkTS project root, do not switch again.
When the `deveco-create-project` skill creates a full project under the current path,
you must switch to that generated project directory before running `build_project` or `start_app`.
Accepts absolute paths and relative paths (resolved from the current workspace directory).

For project-creation requests (新建/创建/scaffold), you MUST first load the `deveco-create-project` skill instead of using this tool to jump to an existing directory. If the target already exists, the skill script will emit `PROJECT_EXISTS` (exit 2) — use `AskUserQuestion` to let the user choose overwrite/rename/cancel.