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/src/verify.rs

@@ -1,10 +1,10 @@
-//! Verifies the whole audit log under a home directory with `proto::ChainVerifier`, reading the
+//! Verifies the whole audit log under a home directory with `bxcore::ChainVerifier`, reading the
 //! files itself so it works when `brokerd` will not start.
 
 use std::io::Write;
 use std::path::Path;
 
-use proto::ChainVerifier;
+use bxcore::ChainVerifier;
 
 /// Verifies the whole audit log under `home` and prints the report to `out`.
 /// `Ok(true)`: the chain verifies. `Ok(false)`: it does not. `Err`: the log cannot be read.
@@ -21,7 +21,7 @@ pub fn run(home: &Path, out: &mut dyn Write) -> std::io::Result<bool> {
                 continue;
             }
         };
-        if proto::is_audit_log_name(&name) {
+        if bxcore::is_audit_log_name(&name) {
             names.push(name);
         } else if name.ends_with(".jsonl") {
             // Looks like a log file but is not named as one: brokerd ignores it too. Say so, so