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/bxcore/tests/log_names.rs

@@ -0,0 +1,38 @@
+//! Which file names are audit log files. `brokerd` and `bxctl audit verify` both use this one rule,
+//! so they always read the same set of files.
+
+use bxcore::is_audit_log_name;
+
+#[test]
+fn a_date_and_jsonl_is_a_log_file() {
+    for name in ["2026-09-17.jsonl", "0000-01-01.jsonl", "9999-12-31.jsonl"] {
+        assert!(is_audit_log_name(name), "{name}");
+    }
+}
+
+#[test]
+fn every_other_name_is_not() {
+    for name in [
+        "",
+        ".lock",
+        "2026-0x-17.jsonl", // the second month digit
+        "2026-x9-17.jsonl",
+        "2026-09-1x.jsonl",
+        "x026-09-17.jsonl",
+        "2026_09-17.jsonl",
+        "2026-09_17.jsonl",
+        "2026-09-17.json",
+        "2026-09-17.jsonl.bak",
+        "2026-9-17.jsonl",
+        "12026-09-17.jsonl",
+        "2026-09-17.JSONL",
+        "２026-09-17.jsonl", // a full-width digit is not an ASCII digit
+        "2026-00-17.jsonl",  // no month 0
+        "2026-13-17.jsonl",
+        "2026-09-00.jsonl", // no day 0
+        "2026-09-32.jsonl",
+        "2026-99-99.jsonl",
+    ] {
+        assert!(!is_audit_log_name(name), "{name}");
+    }
+}