Add farming pool admin transfer

[ProtonsAndElectrons]

Closes #16

Summary

• add a public admin() getter for the farming pool
• add transfer_admin(new_admin) guarded by the current admin and emitting ("pool", "adm_xfr") with (old_admin, new_admin)
• cover successful transfer, non-admin rejection, exact event emission, and old-admin privilege loss after transfer
• update CI/release WASM targets from wasm32-unknown-unknown to wasm32v1-none so Soroban SDK 25 builds on current Rust stable

Notes

• The unauthorized path follows the pool's existing require_auth() admin-gate pattern; the separate typed error refactor appears to be tracked in farming-pool: initialize uses panic! instead of typed PoolError #10.

Validation

• cargo test -p farming-pool
• cargo build --target wasm32v1-none --release
• git diff --check