#13671: fix(memory-lancedb): ship @lancedb/lancedb for bundled extension

## Problem Bundled extensions under `extensions/*` ship in the npm package, but their dependency graphs are not guaranteed to be installed for end users. This caused the bundled `memory-lancedb` extension to break in fresh installs (e.g. `openclaw ltm stats`) when required deps were missing or only available via transitive hoisting. Additionally, workspace-generated `extensions/*/node_modules/.bin/*` artifacts can end up in the packed tarball, and those scripts contain absolute paths from the build machine. ## Fix - Declare `@lancedb/lancedb` at the root as an `optionalDependency` so installs can succeed even on platforms where LanceDB native bindings may not be available. - Declare `openai` at the root so `memory-lancedb` does not rely on transitive hoisting/version drift. - Add a regression test asserting the root declares all `extensions/memory-lancedb` runtime deps. - Add `extensions/.npmignore` to exclude workspace-installed `node_modules` artifacts from the published package. - Minor lint cleanup (remove redundant cast). ## Verification - `pnpm lint` - `pnpm test` - `npm pack --dry-run --json` shows `node_modules entries 0`