Add native Solana support: address derivation, accounts, signing, backfill migration, CloudBackup wiring

Same read/send-capable chain-family pattern as Tron/Bitcoin, but for
Ed25519/SLIP-0010 instead of secp256k1/BIP32 (Solana's account id IS its
raw public key, so no separate address-hash derivation step is needed).

- SLIP-0010 Ed25519 keypair derivation (Bip32Ed25519KeypairFactory),
  cross-validated against an independent slip10 reference implementation
  and pinned to a known-good test vector.
- Chain.isSolanaBased / Chain.Asset.Type.SolanaNative wired through every
  chain-mapper, account-model, and signer dispatch site (mirrors the
  existing Tron/Bitcoin wiring exactly).
- SolanaAddressBackfillMigration derives Solana keys for wallets created
  before this support existed, same self-healing no-stuck-flag design as
  the Tron/Bitcoin backfills - also fixed a latent bug in those two
  migrations where MetaAccountSecrets/MetaAccountLocal.addXAccount()
  dropped sibling chain-family fields on a re-run.
- Room migration 75->76 adds isSolanaBased/solanaPublicKey/solanaAddress
  columns.
- CloudBackup's already-reserved solanaAddress/SolanaSecrets fields are
  now actually read/written by RealLocalAccountsCloudBackupFacade; also
  fixed isCompletelyEmpty() to check solana, so a Solana-only wallet
  doesn't get silently dropped from backup.

feature-cloud-backup-api/src/main/java/io/novafoundation/nova/feature_cloud_backup_api/domain/model/CloudBackup.kt

@@ -285,5 +285,8 @@ data class CloudBackup(
 }
 
 fun CloudBackup.WalletPrivateInfo.isCompletelyEmpty(): Boolean {
-    return entropy == null && substrate == null && ethereum == null && tron == null && bitcoin == null && chainAccounts.isEmpty()
+    // `solana` was missing here already (found while wiring Solana into RealLocalAccountsCloudBackupFacade) -
+    // without it, a wallet whose only secrets were Solana would have been wrongly treated as "completely empty"
+    // and silently dropped from the backup.
+    return entropy == null && substrate == null && ethereum == null && tron == null && bitcoin == null && solana == null && chainAccounts.isEmpty()
 }