proto becomes bxcore, the one shared crate (M5b task 00)

Done the way the owner asked and the spike mapped: the crate and the
manifests renamed, then what the build reported fixed. Layers: 138
"proto unresolved" errors across 169 files; cargo fmt reordering
imports; six fixture paths built as strings in brokerd's and bxctl's
tests, which the compiler cannot see, and comments naming
crates/proto/; the crate-dependency check and its self-test. One more
the spike did not reach: a `\nproto =` key inside a printf format in
the self-test, which a word-boundary replacement skips because `n` and
`p` are both word characters.

make gate: gate: ok, 944 tests; no new entry in /tmp.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

crates/bxctl/src/admin.rs

@@ -4,7 +4,7 @@ use std::io::{self, Write};
 use std::os::unix::net::UnixStream;
 use std::path::{Path, PathBuf};
 
-use proto::{
+use bxcore::{
     Approve, DecisionRecord, DenyReason, Empty, Envelope, ErrorCode, FrameError, Message,
     PROTOCOL_VERSION, PendingApproval, Refuse, Timestamp, WireError, read_frame, write_frame,
 };
@@ -288,10 +288,10 @@ fn session_shown(session: &str) -> String {
 }
 
 // The taint of a decision is its wire name.
-fn taint_name(taint: proto::DataClass) -> &'static str {
+fn taint_name(taint: bxcore::DataClass) -> &'static str {
     match taint {
-        proto::DataClass::Public => "public",
-        proto::DataClass::Private => "private",
-        proto::DataClass::Secret => "secret",
+        bxcore::DataClass::Public => "public",
+        bxcore::DataClass::Private => "private",
+        bxcore::DataClass::Secret => "secret",
     }
 }