Add generic ATProto record retrieval tool
New tool `get_atproto_record` allows fetching any ATProto record by:
- Full AT URI (at://repo/collection/rkey)
- Individual repo, collection, rkey parameters
Supports all ATProto collections (posts, profiles, follows, likes, etc.)
Uses public API first, falls back to authenticated requests if needed.
Returns YAML-formatted record data.
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