AggLayer: Add message bridging

## Description

The Solidity base bridge contract ([`PolygonZkEVMBridgeV2.sol`](https://github.com/agglayer/agglayer-contracts/blob/main/contracts/v2/PolygonZkEVMBridgeV2.sol)) supports two leaf types: `_LEAF_TYPE_ASSET = 0` for token transfers and `_LEAF_TYPE_MESSAGE = 1` for arbitrary cross-chain messages. The bridge provides `bridgeMessage()` and `bridgeMessageWETH()` to create message leaves, and `claimMessage()` to process them with destination contract calls. Critically, `claimAsset()` and `claimMessage()` each enforce the expected leaf type, preventing cross-type claims.

The Miden bridge only handles asset transfers. The [`get_leaf_value`](https://github.com/0xMiden/miden-base/blob/next/crates/miden-agglayer/asm/agglayer/bridge/bridge_in.masm) procedure reads `leafType` from memory and includes it in the Keccak-256 leaf hash computation, but never asserts its value. If a CLAIM note is submitted with `leafType = 1` (a message leaf from the Solidity side), it would be processed as an asset transfer: the origin address (which for messages is `msg.sender`, not a token address) would be used to look up a faucet, potentially minting tokens incorrectly.

While the Merkle proof would still be valid since the leaf hash includes the type byte, the semantic mismatch means a message leaf could trigger incorrect token minting.

## Impact

A message leaf from another chain could be misinterpreted as an asset transfer on Miden, potentially causing a faucet to mint tokens for a cross-chain message that carries no real value. This is a defense-in-depth gap: the Merkle proof validates the data integrity, but not the semantic interpretation.

## Recommended Action

In the `claim` procedure in `bridge_in.masm`, assert that the `leafType` field equals 0 (asset) after loading the leaf data into memory but before verifying the leaf. This prevents message-type leaves from being misinterpreted as asset transfers. The outbound path already hardcodes `leafType = 0`, so no changes are needed there.

## References

- [`bridge_in.masm`](https://github.com/0xMiden/miden-base/blob/next/crates/miden-agglayer/asm/agglayer/bridge/bridge_in.masm)
- [`CLAIM.masm`](https://github.com/0xMiden/miden-base/blob/next/crates/miden-agglayer/asm/note_scripts/CLAIM.masm)
- [`PolygonZkEVMBridgeV2.sol`](https://github.com/agglayer/agglayer-contracts/blob/main/contracts/v2/PolygonZkEVMBridgeV2.sol)

## Classification

Message bridging (`bridgeMessage`/`claimMessage`) is part of the base bridge contract (`PolygonZkEVMBridgeV2`). However, the specific issue here - the missing `leafType` validation in Miden's claim path - is Miden-specific since Solidity enforces leaf types via separate `claimAsset()`/`claimMessage()` functions.