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/policy_redecide.rs

@@ -7,7 +7,7 @@ mod build;
 use brokerd::grants::GrantSet;
 use brokerd::policy::{Ask, Label, Outcome, decide, redecide};
 use build::{grant, now, private, read, secret, set};
-use proto::{DataClass, DenyReason, Mode};
+use bxcore::{DataClass, DenyReason, Mode};
 
 const PATH: &str = "/home/kyle/notes/a.md";
 
@@ -49,7 +49,10 @@ fn auto_now_lets_the_call_run_under_the_grant_that_matches_now() {
     ]);
     let decision = redecide(pending(), &grants, private(), now()).unwrap();
     assert_eq!(decision.grant(), "now-auto");
-    assert_eq!(decision.grant_sha256(), proto::sha256(b"now-auto").unwrap());
+    assert_eq!(
+        decision.grant_sha256(),
+        bxcore::sha256(b"now-auto").unwrap()
+    );
     assert_eq!(decision.matched_path(), Some("/home/kyle"));
     assert_eq!(decision.paths(), ["/home/kyle"]);
     assert_eq!(
@@ -103,7 +106,7 @@ fn a_deny_grant_was_added_while_the_approval_waited() {
     assert_eq!(denial.grant.as_deref(), Some("no-notes"));
     assert_eq!(
         denial.grant_sha256,
-        Some(proto::sha256(b"no-notes").unwrap())
+        Some(bxcore::sha256(b"no-notes").unwrap())
     );
 }