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/loopd/tests/info.rs

@@ -30,7 +30,7 @@ fn props_slots_and_tokenize_read_the_recorded_responses() {
     assert_eq!(props.n_ctx, 131_072);
     assert_eq!(props.total_slots, 2);
     assert_eq!(
-        proto::sha256(props.chat_template.as_bytes())
+        bxcore::sha256(props.chat_template.as_bytes())
             .unwrap()
             .to_hex(),
         "f55f52930aa8bf44ab5cb85f99370fcc3c56e9a85640b812086d5330bce5d86b"