refactor(#2431): extract hive-priv-sock crate from hive-sh4re

Split the priv-socket wire types (PrivRequest/PrivResponse/PrivEvent and
friends) out of hive-sh4re into their own hive-priv-sock crate, mirroring
the existing hive-host-sock split. hive-priv — the root-privileged
helper — now depends on just this narrow protocol crate instead of the
much larger daemon-shared crate, shrinking its dependency surface and
making the privsep boundary easier to audit. No server/client
implementation lives here, only the wire contract; hive-c0re still
depends on hive-sh4re directly for everything else.

hive-c0re/src/dashboard/journal.rs

@@ -74,10 +74,10 @@ pub(super) async fn get_journal(
     };
     match crate::priv_client::read_container_journal(
         &prefixed,
-        hive_sh4re::priv_proto::JournalQuery {
+        hive_priv_sock::JournalQuery {
             lines,
             boot: true,
-            output: hive_sh4re::priv_proto::JournalOutput::ShortIso,
+            output: hive_priv_sock::JournalOutput::ShortIso,
             unit,
             ..Default::default()
         },