merge: reconcile with feature/trc20-tron-send into one combined branch

Bitcoin was branched off main independently instead of continuing on top
of the Tron send branch, which caused real divergence: both branches touch
the same shared signing/DI code (multiChainEncryptionFor, getMetaAccountKeypair,
NodeHealthStateTesterFactory, AssetsModule/TypeBasedAssetSourceRegistry,
CloudBackup schema, Fee model), and both need to ship together in one
coordinated release once wallet-util's master is unblocked. Merging now
reconciles that before it gets any harder, and gives one branch/versionCode
history for device testing instead of two that silently diverge.

Conflict resolutions of note:
- SecretStoreV2/SecretsSigner: getKeypair and multiChainEncryptionFor now
  recognize Tron AND Bitcoin accounts (isTronBased/isBitcoinBased both
  threaded through, checked before the Ethereum fallback).
- AccountDataSourceImpl: both address-backfill migrations now run
  sequentially in one coroutine (Tron's fix for a race against the legacy
  migration applies equally to Bitcoin's backfill).
- CloudBackup: kept Tron's forward-looking Solana schema reservation
  alongside Tron's and Bitcoin's now-real fields.
- ChainRegistryModule/NodeHealthStateTesterFactory: adopted Tron's
  self-contained short-lived OkHttpClient (simpler than threading the
  shared app-wide client through RuntimeDependencies, which is reverted).
- RealSecretsMetaAccount: extended Tron's chain-account MultiChainEncryption
  fix to also cover Bitcoin, for the same underlying reason.
- ChainExt.isValidAddress: Tron's branch independently closed the
  pre-existing Tron validation gap; kept alongside Bitcoin's own check.

feature-account-api/src/main/java/io/novafoundation/nova/feature_account_api/data/model/Fee.kt

@@ -75,6 +75,19 @@ class BitcoinFee(
     override val asset: Chain.Asset
 ) : Fee
 
+/**
+ * Fee for a Tron transaction (native TRX or TRC-20), always denominated in TRX (sun), regardless of which asset
+ * is being sent - Tron has no separate "gas token" concept, network resources (bandwidth/energy) are always
+ * burned as TRX. [amount] is this client's own estimate of that burn (see `RealTronTransactionService`); the
+ * network only ever burns what it actually uses, so the real cost can be lower, but never higher than what this
+ * client authorized via `fee_limit` when submitting.
+ */
+class TronFee(
+    override val amount: BigInteger,
+    override val submissionOrigin: SubmissionOrigin,
+    override val asset: Chain.Asset
+) : Fee
+
 class SubstrateFeeBase(
     override val amount: BigInteger,
     override val asset: Chain.Asset