GETEMAIL (auspex) lists accounts whose email matches a glob. SET
RESTRICTED makes a channel kick anyone without access (or oper) as they
join, mirroring the SECUREOPS on-join enforcement.
SET <#channel> SUCCESSOR <account>|OFF names an account that inherits the
channel if the founder's account is dropped or expires, instead of the
channel being released. Adds a ChannelInfo.successor field + event, and
centralises the founder-gone channel release into a single
release_founded_channels store method used by DROP, expiry, and the
gossip account-gone path so all three transfer consistently.
CANCEL recalls the sender's most recent unread memo to a target (one the
recipient already read can't be recalled); CHECK reports whether the last
memo you sent someone has been read; INFO summarises your mailbox. Adds
memo_cancel/memo_check store methods and shares MAX_MEMOS from the module
root instead of duplicating it in send.rs.
engine/db.rs had grown past 4k lines. Split the single Db type's
operations into sibling files by domain — account, channel, network,
the event log, and the module-facing store facade — while all type
definitions, the log plumbing, and shared helpers stay in db/mod.rs.
Pure reorganisation: no behaviour change, tests unchanged and green.
