feat(anvil): seed Base activation features for a standalone anvil --base node (BOP-375)

[amiecorso]

What

A standalone anvil --base node now has Base's activation-gated features (B20Asset, B20Stablecoin, PolicyRegistry) active at startup, matching forge --base local execution and a live Beryl-or-later chain.

Why

--base installs the Base precompiles, but the gated features start OFF in a fresh local EVM. forge --base already seeds them active for local (non-fork) runs; a node a developer starts with anvil --base did not, so calls reverted FeatureNotActivated until the dev manually activate()d each feature over RPC.

How

In Backend::apply_genesis, after the genesis alloc, write NetworkConfigs::base_activation_seeds() into the node DB via set_storage_at. Reuses the exact seeds + derivation as the forge path. Skipped in fork mode (the live chain carries real activation state); no-op unless --base is set.

Verification

• cargo check -p anvil clean.
• anvil --base: isActivated(bytes32) returns true for B20Asset / B20Stablecoin / PolicyRegistry with no manual activate(); a bogus feature id returns false.
• plain anvil: registry has no code (unchanged behavior).

Closes BOP-375.

[linear]

BOP-375