release(core+gemini): bump to 0.17.0

- Removed the temporary @headless-coder-sdk/gemini-adapter dependency from core.
- Bumped core and the gemini adapter to 0.17.0, and aligned all adapter peer dependencies to ^0.17.0.
- Added a 0.17.0 changelog entry and regenerated the pnpm lockfile.
- Verified via npm run acp:e2e.

release(core+gemini): prepare v0.16.0

- Added richer Gemini tool events to the shared type definitions and docs.
- Updated the repo and core READMEs with the canonical multi-provider example.
- Bumped @headless-coder-sdk/core and @headless-coder-sdk/gemini-adapter to 0.16.0 (core now depends on the new Gemini version) and refreshed the changelog plus pnpm lockfile.

docs(core): add package metadata

Committed the package-specific README and LICENSE files under packages/core as provided.

docs(changelog): add 0.11.0 release notes

Documented the v0.11.0 release with highlights around adapter improvements, new tests, and packaging cleanup.