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/loopd/tests/baseline.rs

@@ -2,10 +2,10 @@
 
 mod support;
 
+use bxcore::{CallId, DataClass, Epoch, Hash32, LogRecord, SessionId, Timestamp, ToolCall};
 use loopd::baseline::{Baseline, messages};
 use loopd::llama::ChatMessage;
 use loopd::tools::Registry;
-use proto::{CallId, DataClass, Epoch, Hash32, LogRecord, SessionId, Timestamp, ToolCall};
 use std::path::Path;
 use support::Home;
 
@@ -67,7 +67,7 @@ fn json_round_trip_and_hash() {
     assert_eq!(Baseline::from_json(&text).unwrap(), b);
     assert_eq!(
         b.hash().unwrap(),
-        proto::sha256(text.as_bytes()).unwrap(),
+        bxcore::sha256(text.as_bytes()).unwrap(),
         "the hash is of the JSON as written"
     );
     assert_ne!(b.hash().unwrap(), Hash32::ZERO);