Implements AnthropicAdapter using the anthropic SDK.
- Reads ANTHROPIC_API_KEY from env; raises ValueError if missing
- resolve_model() looks up capability_map in team.yaml config,
falls back to "capable" tier then hard-coded claude-sonnet-4-6
- complete() supports system_prompt, max_tokens (default 4096),
and temperature (default 0) via the context dict
- Adds PyGithub to requirements.txt (needed by GitHubAdapter)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
