Summary

Implement Move framework changes for Bitcoin header-only import mode. This is a sub-issue of #3922.

Tasks

1. Modify execute_l1_block to skip transaction processing

• Modify execute_l1_block in bitcoin.move to directly call process_block_header
• Skip pending_block::add_pending_block and transaction processing
• Keep timestamp update logic
• Add new entry function execute_l1_block_header for future use by Relayer

2. Add Merkle proof verification module

Create merkle_proof.move with:

• MerkleProof and ProofNode data structures in types.move
• verify_merkle_proof(tx_hash, merkle_root, proof) function
• verify_tx_in_block(block_hash, tx, proof) function
• May need to add sha256d_concat helper in bitcoin_hash.move

3. Implement minimal submit_tx_with_proof

public entry fun submit_tx_with_proof(
    block_hash: address, 
    tx_bytes: vector<u8>, 
    proof_bytes: vector<u8>
) {
    // 1. Parse transaction and proof
    // 2. Verify Merkle proof
    // 3. Emit verification success event
    // Note: UTXO creation will be added in future versions
}

4. Unit tests

• Test Merkle proof verification with valid/invalid proofs
• Test execute_l1_block_header functionality
• Test submit_tx_with_proof verification

Files to modify

• frameworks/bitcoin-move/sources/bitcoin.move
• frameworks/bitcoin-move/sources/types.move
• frameworks/bitcoin-move/sources/bitcoin_hash.move (if needed)
• New: frameworks/bitcoin-move/sources/merkle_proof.move

Acceptance Criteria

• New blocks no longer create UTXO objects
• Timestamp updates still work correctly
• Merkle proof verification passes unit tests
• submit_tx_with_proof can verify transaction inclusion

Parent Issue

#3922