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%.
