- Add common.proto with Empty, StringMap, and AppError messages
- Add user.proto with User message (34 fields mirroring model.User)
- Add channel.proto with Channel, ChannelType enum, ChannelBannerInfo
- Add post.proto with Post, PostMetadata, PostEmbed, PostPriority, Reaction
- Add team.proto with Team, TeamMember, TeamUnread, TeamType enum
- Add file.proto with FileInfo, FileUploadResponse, FileData
- Update Makefile to support all proto files with proper import mappings
- Remove bootstrap.proto (replaced by common.proto)
- Use google.protobuf.Struct for dynamic JSON fields (Post.props, Channel.props)
- All timestamps are int64 (milliseconds since epoch)
- All IDs are strings (26-char base32)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
