#22504: chore: remove unused Teams hosting deps

## Summary - Remove unused Microsoft Teams extension dependencies (`@microsoft/agents-hosting-express`, `@microsoft/agents-hosting-extensions-teams`) from `extensions/msteams/package.json`. - Point A2UI rolldown alias resolution for lit/context/signals directly at the `ui` workspace dependency tree. - Add `rolldown` fallback in `scripts/bundle-a2ui.sh` when the binary is not on PATH. ## Validation - `pnpm deadcode:report:ci:knip` generated artifacts and no longer reports these Teams deps as unused in this tranche. - `pnpm install --lockfile-only` refreshed lockfile dependencies.