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/bxctl/tests/verify.rs

@@ -1,4 +1,4 @@
-//! `bxctl audit verify` against the fixture logs in `crates/proto/tests/fixtures/audit/`.
+//! `bxctl audit verify` against the fixture logs in `crates/bxcore/tests/fixtures/audit/`.
 //! Do not edit. The output is compared byte for byte: the owner reads it, and so do scripts.
 
 use std::path::PathBuf;
@@ -20,7 +20,7 @@ impl Home {
         let audit = path.join("audit");
         std::fs::create_dir_all(&audit).unwrap();
         let from = format!(
-            "{}/../proto/tests/fixtures/audit/{case}",
+            "{}/../bxcore/tests/fixtures/audit/{case}",
             env!("CARGO_MANIFEST_DIR")
         );
         for entry in std::fs::read_dir(&from).unwrap_or_else(|e| panic!("{from}: {e}")) {
@@ -49,11 +49,11 @@ fn run(case: &str) -> (bool, String) {
 /// The hex of the hash of the last line of `file` in `case`.
 fn head_of(case: &str, file: &str) -> String {
     let path = format!(
-        "{}/../proto/tests/fixtures/audit/{case}/{file}",
+        "{}/../bxcore/tests/fixtures/audit/{case}/{file}",
         env!("CARGO_MANIFEST_DIR")
     );
     let text = std::fs::read_to_string(path).unwrap();
-    proto::sha256(text.lines().last().unwrap().as_bytes())
+    bxcore::sha256(text.lines().last().unwrap().as_bytes())
         .unwrap()
         .to_hex()
 }