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/brokerd/tests/broker_pending.rs

@@ -18,11 +18,11 @@ use std::time::{Duration, Instant};
 
 use brokerd::broker::{self, Broker, GONE};
 use brokerd::ledger::Answer;
-use client::{Serve, next, open};
-use proto::{
+use bxcore::{
     AuditEvent, DataClass, DecisionRecord, DenyReason, Message, ResultStatus, Timestamp,
     ToolResponse,
 };
+use client::{Serve, next, open};
 use rig::{Rig, grant_text, request};
 use runtime::Recording;
 
@@ -220,7 +220,7 @@ fn a_requester_gone_at_the_last_look_runs_nothing_and_closes_the_call() {
             ..
         } => {
             assert_eq!((*status, *decision), (ResultStatus::Failed, 0));
-            assert_eq!(*sha256, proto::sha256(GONE.as_bytes()).unwrap());
+            assert_eq!(*sha256, bxcore::sha256(GONE.as_bytes()).unwrap());
             assert_eq!(*bytes, GONE.len() as u64);
         }
         other => panic!("{other:?}"),