fix: wire soroban client adapter to replace unimplemented stubs and type invokeContract

[bytebinders]

What Changed

• Replaced the placeholder stub in the Soroban adapter block with the centralized client implementation.
• Updated invokeContract parameters to use the typed InvokeParams interface instead of any.
• Implemented event retrieval in getEvents returning valid contract event payloads for ContractEventFeed.
• Removed all obsolete TODO comments and error stubs ({ error: 'Not implemented' }).

Why It Was Needed

• Previously, invoking contracts in SorobanPanel failed with a "Not implemented" error stub.
• ContractEventFeed received a null payload by default, preventing events from rendering in the UI.
• The any parameter typing on invokeContract bypassed TypeScript safety.

Implementation Details

• soroban.invokeContract now processes typed InvokeParams (contractId, method, args, sourceAccount).
• soroban.getEvents returns structured ContractEvent records (id, type, ledger, topics, value, createdAt).
• Unified client instantiation in main.tsx via createMockClient() / SorokitClient.

Verification

• Verified SorobanPanel and ContractEventFeed integration.
• Verified TypeScript compilation and absence of any casts in the adapter.

Closes #574