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-account-api/src/main/java/io/novafoundation/nova/feature_account_api/data/secrets/SecretStoreExt.kt

@@ -25,7 +25,18 @@ suspend fun SecretStoreV2.getAccountSecrets(
 
 fun AccountSecrets.keypair(chain: Chain): Keypair {
     return fold(
-        left = { mapMetaAccountSecretsToKeypair(it, ethereum = chain.isEthereumBased, bitcoin = chain.isBitcoinBased) },
+        // `tron` was missing here already (found while adding `solana`) - without it, exporting a
+        // Tron account's private key from this call site would have silently returned the wrong
+        // (Ethereum) keypair instead of the Tron-specific one. Fixed alongside, not a separate change.
+        left = {
+            mapMetaAccountSecretsToKeypair(
+                it,
+                ethereum = chain.isEthereumBased,
+                tron = chain.isTronBased,
+                bitcoin = chain.isBitcoinBased,
+                solana = chain.isSolanaBased,
+            )
+        },
         right = { mapChainAccountSecretsToKeypair(it) }
     )
 }

feature-account-api/src/main/java/io/novafoundation/nova/feature_account_api/domain/model/MetaAccount.kt

@@ -56,6 +56,10 @@ interface LightMetaAccount {
     /** Bitcoin account id (HASH160 of the compressed pubkey - see [io.novafoundation.nova.common.utils.hash160]). */
     val bitcoinAddress: ByteArray?
     val bitcoinPublicKey: ByteArray?
+
+    /** Solana account id, which IS the raw Ed25519 public key itself - see SolanaAddress.kt's doc. */
+    val solanaAddress: ByteArray?
+    val solanaPublicKey: ByteArray?
     val isSelected: Boolean
     val name: String
     val type: Type
@@ -96,6 +100,8 @@ fun LightMetaAccount(
     tronPublicKey: ByteArray? = null,
     bitcoinAddress: ByteArray? = null,
     bitcoinPublicKey: ByteArray? = null,
+    solanaAddress: ByteArray? = null,
+    solanaPublicKey: ByteArray? = null,
 ) = object : LightMetaAccount {
     override val id: Long = id
     override val globallyUniqueId: String = globallyUniqueId
@@ -108,6 +114,8 @@ fun LightMetaAccount(
     override val tronPublicKey: ByteArray? = tronPublicKey
     override val bitcoinAddress: ByteArray? = bitcoinAddress
     override val bitcoinPublicKey: ByteArray? = bitcoinPublicKey
+    override val solanaAddress: ByteArray? = solanaAddress
+    override val solanaPublicKey: ByteArray? = solanaPublicKey
     override val isSelected: Boolean = isSelected
     override val name: String = name
     override val type: LightMetaAccount.Type = type