hive-sh4re: split inbox, container, journal, and schedule wire shapes into their own modules

Closes the #3110 split — lib.rs is now just the crate doc comment and
the pub mod list.

journal.rs's new doc comment fixes a pre-existing bug: the old
JournalPriority doc text in lib.rs was actually half Capability's doc
(a leftover from an earlier reorder that moved the code but not the
comment above it).

hive-host-sock/src/lib.rs

@@ -12,8 +12,8 @@
 
 use std::path::PathBuf;
 
-use hive_sh4re::AgentStatusRow;
 use hive_sh4re::approvals::Approval;
+use hive_sh4re::container::AgentStatusRow;
 use hive_types::Ident;
 use serde::{Deserialize, Serialize};