test(crypto): replace the one-file key scan with a repo-wide guard

crates/crypto/src/license_token.rs asserted, via include_str! on its own
file, that the license-token signing key is never checked in. The scan saw
exactly one file: the key moved anywhere else passed silently, and renaming
license_token.rs stopped the guard from compiling instead of reporting.

scripts/check_embedded_secrets.sh scans every tracked and not-yet-added text
file for the same needle plus the other private-key header forms and eleven
provider credential formats, and it does not skip the paths
.github/secret_scanning.yml tells push protection to ignore. Non-secret
matches are excused by exact literal, never by path glob, and an exemption
that stops matching is reported as stale. --self-test asserts every pattern
family fires.

crates/crypto/src/license_token.rs

@@ -203,14 +203,6 @@ mod tests {
         assert!(result.is_err());
     }
 
-    #[test]
-    fn test_source_does_not_embed_private_key() {
-        let source = include_str!("license_token.rs");
-        let forbidden = ["BEGIN", "PRIVATE KEY"].join(" ");
-
-        assert!(!source.contains(&forbidden));
-    }
-
     #[test]
     fn test_parse_signed_license_token_rejects_invalid_token() {
         let mut rng = rand::rng();