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.rs

@@ -20,18 +20,18 @@ use std::sync::Arc;
 use brokerd::broker;
 use brokerd::ledger::NOT_RECORDED;
 use brokerd::runner::{REFUSING, RunError};
-use client::{Serve, call, next, open};
-use proto::{
+use bxcore::{
     ApprovalList, Approve, ApproveResult, AuditEvent, DataClass, DecisionRecord, DenyReason, Empty,
     Envelope, ErrorCode, GrantsReport, Message, Refuse, ResultStatus, SessionId, ToolResponse,
     Turn, TurnDone, TurnEvent, Usage, WireError,
 };
+use client::{Serve, call, next, open};
 use rig::{Rig, grant_text, request};
 use runtime::Recording;
 
 const NOTES: &str = r#"{"path":"/n/a"}"#;
 
-fn read_notes(call_id: u64) -> proto::ToolRequest {
+fn read_notes(call_id: u64) -> bxcore::ToolRequest {
     request("s1", call_id, "read_file", NOTES)
 }