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/tests/chat_approvals.rs

@@ -5,10 +5,10 @@
 
 mod support;
 
-use bxctl::chat::{Approvals, OnPending, Printer, TurnIo, handle_pending, stream_turn};
-use proto::{
+use bxcore::{
     Approve, DecisionRecord, Empty, ErrorCode, Message, Refuse, SessionId, Timestamp, TurnEvent,
 };
+use bxctl::chat::{Approvals, OnPending, Printer, TurnIo, handle_pending, stream_turn};
 use std::io::{BufRead, Cursor, Write};
 use std::path::Path;
 use std::process::{Command, Stdio};
@@ -178,7 +178,7 @@ fn a_brokerd_that_cannot_be_reached_is_reported_and_nothing_is_asked() {
 #[test]
 fn an_answer_that_comes_too_late_is_reported() {
     let fake = fake_brokerd(|msg| match msg {
-        Message::Approvals(_) => Message::ApprovalList(proto::ApprovalList {
+        Message::Approvals(_) => Message::ApprovalList(bxcore::ApprovalList {
             items: vec![pending(41, "shell", "{}")],
         }),
         _ => wire_error(ErrorCode::NoSuchApproval, "no such approval"),
@@ -204,7 +204,7 @@ fn an_answer_that_comes_too_late_is_reported() {
 #[test]
 fn an_answer_that_fails_is_reported_and_is_not_an_error() {
     let fake = fake_brokerd(|msg| match msg {
-        Message::Approvals(_) => Message::ApprovalList(proto::ApprovalList {
+        Message::Approvals(_) => Message::ApprovalList(bxcore::ApprovalList {
             items: vec![pending(41, "shell", "{}")],
         }),
         _ => wire_error(ErrorCode::Internal, "boom"),