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.

common/build.gradle

@@ -9,7 +9,7 @@ android {
         buildConfigField "String", "TERMS_URL", "\"https://pezkuwichain.io/terms.html\""
         buildConfigField "String", "GITHUB_URL", "\"https://github.com/pezkuwichain\""
         buildConfigField "String", "TELEGRAM_URL", "\"https://t.me/pezkuwichainBot\""
-        buildConfigField "String", "TWITTER_URL", "\"https://twitter.com/pezkuwichain\""
+        buildConfigField "String", "TWITTER_URL", "\"https://x.com/bizinikiwi\""
         buildConfigField "String", "RATE_URL", "\"market://details?id=${rootProject.applicationId}.${releaseApplicationSuffix}\""
         buildConfigField "String", "EMAIL", "\"support@pezkuwichain.io\""
         buildConfigField "String", "YOUTUBE_URL", "\"https://www.youtube.com/@SatoshiQazi\""