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/src/grants.rs

@@ -8,7 +8,7 @@
 use std::path::Path;
 
 use crate::args::{ToolName, valid_host_pattern, valid_path};
-use proto::{DataClass, Grant, GrantProblem, Mode, sha256};
+use bxcore::{DataClass, Grant, GrantProblem, Mode, sha256};
 
 /// Where the owner reads the rules behind a rejected set.
 pub const RUNBOOK: &str = "see docs/runbook.md#grants-invalid";
@@ -17,8 +17,8 @@ pub const RUNBOOK: &str = "see docs/runbook.md#grants-invalid";
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct LoadedGrant {
     pub id: String, // the file stem
-    pub grant: proto::Grant,
-    pub sha256: proto::Hash32, // of the file's bytes as read
+    pub grant: bxcore::Grant,
+    pub sha256: bxcore::Hash32, // of the file's bytes as read
 }
 
 /// A set that passed every rule, in id order. Its field is private: `from_grants` and `load` are