Use genesis hash in filename instead of cluster prefix

[Copilot]

Genesis files were named by cluster (mainnet-genesis.bin, testnet-genesis.bin), which doesn't disambiguate between different genesis configurations.

Changes

• fd_config.c: Generate path as genesis-{hash}.bin using consensus.expected_genesis_hash directly instead of mapping to cluster prefix
• default.toml: Update documentation to reflect new naming pattern
• Fallback to genesis-local.bin when hash is empty/null

Example

Before:

/home/fire/.firedancer/fd1/mainnet-genesis.bin

After:

/home/fire/.firedancer/fd1/genesis-5eykt4UsFv8P8NJdTREpY1vzqKqZKvdpKuc147dw2N9d.bin

Original prompt

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This section details on the original issue you should resolve

<issue_title>Naming pattern genesis-[hash].bin</issue_title>
<issue_description>Instead of mainnet-genesis.bin, call blobs genesis-[hash].bin to disambiguate</issue_description>

<agent_instructions>Keep comments minimal </agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Naming pattern genesis-[hash].bin #8607

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