test: repair stale test fixtures across identity, mesh, update, wallet, fips

Several tests had drifted from the current production behavior:

- identity_manager: create() already auto-provisions a Nostr key, so the
  explicit create_nostr_key() call failed with "already exists". Rewrite
  the test to assert on record.nostr_npub from create() directly.
- mesh/protocol: test_build_app_start read the app name from frame[4..]
  but the v2 layout is [0:marker][1-2:len][3:cmd][4:version][5..:name].
  test_identity_broadcast_roundtrip expected input DID = output DID but
  the v2 decoder derives DID from the ed25519 pubkey, so the roundtrip
  compares against did_key_from_pubkey_hex(&pub) now.
- mesh/bitcoin_relay: test_build_block_header_announcement asserted
  sig.is_some(), but the builder intentionally emits an unsigned envelope
  to fit the 160-byte LoRa limit; assert sig.is_none(). Also widen
  placeholder hashes to the required 64 hex chars (32 bytes).
- update: load_mirrors() now merges default mirrors post-migration, so
  the roundtrip test must assert the custom mirror survives alongside
  the defaults rather than strict equality.
- wallet/cashu: test_proof_c_as_pubkey used hex that is not on the curve;
  replace with the secp256k1 generator point G so parsing succeeds.
- fips: test_status_reports_no_key_pre_onboarding asserted npub.is_none(),
  which fails on dev boxes where the fips daemon is already running. Keep
  the !key_present assertion and drop the npub one.

core/archipelago/src/mesh/protocol.rs

@@ -701,9 +701,11 @@ mod tests {
 
     #[test]
     fn test_build_app_start() -> Result<()> {
+        // Frame layout: [0: '>'][1-2: len LE][3: CMD][4: VERSION][5..: padded name]
         let frame = build_app_start("Archipelago");
         assert_eq!(frame[3], CMD_APP_START);
-        let name = &frame[4..];
+        assert_eq!(frame[4], PROTOCOL_VERSION);
+        let name = &frame[5..];
         assert_eq!(
             std::str::from_utf8(name)
                 .map_err(|e| anyhow::anyhow!("invalid UTF-8 in app name: {}", e))?,
@@ -753,15 +755,20 @@ mod tests {
 
     #[test]
     fn test_identity_broadcast_roundtrip() -> Result<()> {
-        let did = "did:key:z6MkhaXgBZDvotDkL5257faiztiGiC2QtKLGpbnnEGta2doK";
+        // The v2 encoding drops the DID and the decoder reconstructs it
+        // deterministically from the ed25519 pubkey, so the roundtripped
+        // DID won't equal an arbitrary input DID. Derive what the decoder
+        // will produce and assert against that.
         let ed_pub = "a".repeat(64);
         let x25519_pub = "b".repeat(64);
+        let expected_did = crate::identity::did_key_from_pubkey_hex(&ed_pub)
+            .map_err(|e| anyhow::anyhow!("derive did: {}", e))?;
 
-        let encoded = encode_identity_broadcast(did, &ed_pub, &x25519_pub);
+        let encoded = encode_identity_broadcast(&expected_did, &ed_pub, &x25519_pub);
 
         let (parsed_did, parsed_ed, parsed_x) = parse_identity_broadcast(&encoded)
             .ok_or_else(|| anyhow::anyhow!("failed to parse identity broadcast"))?;
-        assert_eq!(parsed_did, did);
+        assert_eq!(parsed_did, expected_did);
         assert_eq!(parsed_ed, ed_pub);
         assert_eq!(parsed_x, x25519_pub);
         Ok(())