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-agent/src/serve_common.rs

@@ -27,9 +27,9 @@ pub fn format_wake_prompt(
     interrupted: bool,
 ) -> String {
     let banner = if redelivered {
-        hive_sh4re::REDELIVERY_HINT
+        hive_sh4re::inbox::REDELIVERY_HINT
     } else if interrupted {
-        hive_sh4re::INTERRUPTED_HINT
+        hive_sh4re::inbox::INTERRUPTED_HINT
     } else {
         ""
     };
@@ -38,7 +38,7 @@ pub fn format_wake_prompt(
     } else {
         String::new()
     };
-    let pending = hive_sh4re::pending_hint(unread);
+    let pending = hive_sh4re::inbox::pending_hint(unread);
     format!("{banner}{tag}Incoming message from `{from}`:\n---\n{body}\n---{pending}")
 }