Extract business logic from handleMsgMhfOperateGuildMember into
GuildService.OperateMember, establishing the handler→service→repo
layering pattern. The handler is now ~20 lines of protocol glue
(type-assert, map action, call service, send ACK, notify).
GuildService owns authorization checks, repo coordination, mail
composition, and best-effort mail delivery. It accepts plain Go
types (no mhfpacket or Session imports), making it fully testable
with mock repos. Cross-channel notification stays in the handler
since it requires Session.
Adds 7 table-driven service-level tests covering accept/reject/kick,
authorization, repo errors, mail errors, and unknown actions.
Cover the 4 handler files that had no tests: handlers_guild_ops.go,
handlers_guild_scout.go, handlers_guild_board.go, and handlers_items.go.
44 new tests exercise the error-logging paths added in 8fe6f60 and the
core handler logic (disband, resign, apply, leave, accept/reject/kick,
scout answer, message board CRUD, weekly stamps, item box parsing).
New mock types: mockGuildRepoOps (enhanced guild repo with configurable
errors and state tracking), mockUserRepoForItems, mockStampRepoForItems,
mockHouseRepoForItems. Coverage rises from 41.1% to 43.7%.
