solana-staking: update deposit-to-specific-validator example for mandatory ephemeral_seed (staker breaking change)

[cpascoli]

Context

The SOL staker program has a breaking change from TruFin-io/smart-contracts-solana#147 (ephemeral-seed poisoning DoS fix). deposit_to_specific_validator now takes a required ephemeral_seed: u64 argument, and the ephemeral stake account must be the PDA derived from that seed.

Devnet was upgraded on 2026-07-24 (program 6EZAJVrNQdnBJU6ULxXSDaEoK6fN7C3iXTCkZKRWDdGM), so the published example no longer works as written.

What to change

In packages/solana-staking:

1. src/scripts/anchor/deposit-to-specific-validator.ts — generate a fresh random u64 seed per call, derive the ephemeral stake account PDA under the SPL Stake Pool program (seeds = ["ephemeral", stake_pool_pubkey, seed as u64 LE (8 bytes)]), pass the seed as the second instruction argument and the PDA as ephemeralStakeAccount.
2. src/idl/staker.json — refresh to the new IDL.
3. src/docs/deposit-to-specific-validator.md — update the walkthrough to explain the seed: it must be random/fresh on every call so the pool-global ephemeral address is never fixed (that is the point of the DoS fix — a poisoned address is simply abandoned by choosing a different seed).

Reference

Working version: scripts/deposit-to-specific-validator.ts in TruFin-io/smart-contracts-solana.