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/escape_details.rs

@@ -1,9 +1,9 @@
 //! Text from `brokerd` or the inference server is escaped like model text before it reaches the
 //! terminal: a `retrying` error and every error detail (M3a review finding 10).
 
+use bxcore::{ErrorCode, TurnEvent, WireError};
 use bxctl::admin::AdminError;
 use bxctl::chat::{ChatError, Printer};
-use proto::{ErrorCode, TurnEvent, WireError};
 
 const ESC: char = '\u{1b}';
 
@@ -61,13 +61,13 @@ fn an_error_detail_is_escaped_in_chat_and_admin_errors() {
 #[test]
 fn a_frame_error_is_escaped() {
     let bad = r#"{"v":1,"id":1,"final":true,"msg":{"kind":"\u001b[2J\u202e"}}"#;
-    let error = serde_json::from_str::<proto::Envelope>(bad).unwrap_err();
+    let error = serde_json::from_str::<bxcore::Envelope>(bad).unwrap_err();
     for text in [
-        ChatError::Frame(proto::FrameError::Json(
-            serde_json::from_str::<proto::Envelope>(bad).unwrap_err(),
+        ChatError::Frame(bxcore::FrameError::Json(
+            serde_json::from_str::<bxcore::Envelope>(bad).unwrap_err(),
         ))
         .to_string(),
-        AdminError::Frame(proto::FrameError::Json(error)).to_string(),
+        AdminError::Frame(bxcore::FrameError::Json(error)).to_string(),
     ] {
         clean(&text);
         assert!(text.contains("\\u001b"), "{text}");