attached: filter EVM chains with invalid native currency symbol

[Ryz0nd]

Summary

OkoEIP1193Provider validates every chain's nativeCurrency.symbol against a
1-8 character constraint (validateNativeCurrencySymbol in
sdk/oko_sdk_eth/src/utils/utils.ts). If a single chain fails, the constructor
throws and the entire EVM provider fails to initialize — breaking getAccounts
and downstream wallet flows for every integrator, even on chains they don't use.

The Keplr chain registry currently exposes two EVM entries whose coinDenom
exceeds the limit:

• eip155:1611 — NVNM Mainnet EVM (MANTRAUSD, 9 chars)
• eip155:787111 — NVNM Testnet EVM (MANTRAUSD, 9 chars)

These were enough to crash OkoEthWallet.getEthereumProvider() on
app.civitia.org, which surfaced as Oko "not loading" before Google sign-in.

This hotfix filters such chains out inside handleGetEthChain so they never
reach the SDK validator. Only attached.oko.app needs to be redeployed —
integrators do not need to ship a new SDK build. A follow-up that hardens the
SDK itself (skipping invalid chains rather than rejecting the whole provider)
can land separately.