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/gatewayd/src/ws/handshake.rs

@@ -34,11 +34,11 @@ pub fn base64(bytes: &[u8]) -> String {
 
 /// The `Sec-WebSocket-Accept` a server must send for `key`.
 pub fn accept_for(key: &str) -> String {
-    // base64(sha1(key + GUID)), with `proto::sha1::sha1`.
+    // base64(sha1(key + GUID)), with `bxcore::sha1::sha1`.
     let mut data = Vec::with_capacity(key.len() + GUID.len());
     data.extend_from_slice(key.as_bytes());
     data.extend_from_slice(GUID.as_bytes());
-    base64(&proto::sha1::sha1(&data))
+    base64(&bxcore::sha1::sha1(&data))
 }
 
 /// A fresh key: 16 bytes from `random` (in `gatewayd`, `/dev/urandom`), in base64.