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/memory.rs

@@ -9,13 +9,13 @@ use std::path::PathBuf;
 use std::sync::{Arc, Mutex};
 use std::time::Duration;
 
+use bxcore::{
+    Envelope, ErrorCode, Message, PROTOCOL_VERSION, SessionId, Turn, read_frame, write_frame,
+};
 use loopd::channel::{Context, serve};
 use loopd::llama::Client;
 use loopd::memory::{MemorySource, UNAVAILABLE};
 use loopd::tools::Registry;
-use proto::{
-    Envelope, ErrorCode, Message, PROTOCOL_VERSION, SessionId, Turn, read_frame, write_frame,
-};
 use support::{FakeServer, Home, Reply, ScriptedPort};
 
 const CHAT: &str = "/v1/chat/completions";