Add read-only Tron (TRC20) chain family support (#9)

* Add read-only Tron (TRC20) chain family support

Adds Tron as a third chain family alongside Substrate and EVM:
address derivation (BIP44 coin type 195, secp256k1 reused from the
existing Ethereum path, Base58Check encoding), TronGrid-backed TRX
and TRC20 USDT balance display, and a Room migration for the new
per-account Tron key/address columns. Read-only only — no send,
signing, or broadcast support yet.

* fix: exhaustive when branches for Trc20/TronNative asset types

ChainExt.kt's onChainAssetId and Common.kt's existentialDepositError
both switch exhaustively over Chain.Asset.Type and didn't have cases
for the new Trc20/TronNative variants, breaking compilation. Trc20
mirrors EvmErc20 (contract address as the on-chain id, dust burns
rather than transfers on removal); TronNative mirrors EvmNative.

feature-settings-impl/src/main/java/io/novafoundation/nova/feature_settings_impl/domain/utils/CustomChainFactory.kt

@@ -124,6 +124,7 @@ class CustomChainFactory(
             legacyAddressPrefix = null,
             types = prefilledChain?.types,
             isEthereumBased = isEthereumBased,
+            isTronBased = false,
             isTestNet = prefilledChain?.isTestNet.orFalse(),
             source = Chain.Source.CUSTOM,
             hasSubstrateRuntime = hasSubstrateRuntime,