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/priv_client.rs

@@ -7,7 +7,7 @@
 //! a persistent connection.
 
 use anyhow::{Context as _, Result, bail};
-use hive_sh4re::priv_proto::{
+use hive_priv_sock::{
     BindMount, CredentialMount, InfraAction, InfraContainer, JournalQuery, NetworkIsolation,
     PRIV_SOCK, PrivEvent, PrivRequest, PrivResponse, PrivStream,
 };