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/support/turn.rs

@@ -5,12 +5,12 @@
 #![allow(dead_code)]
 
 use crate::support::{FakeServer, Home, ScriptedPort};
+use bxcore::{LogRecord, SessionId, ToolResponse, TurnEvent};
 use loopd::baseline::Baseline;
 use loopd::llama::Client;
 use loopd::session::Session;
 use loopd::tools::Registry;
 use loopd::turn::{Runtime, TurnError, run_turn};
-use proto::{LogRecord, SessionId, ToolResponse, TurnEvent};
 
 pub struct Setup {
     pub home: Home,