CLPR-8.3: Ethereum Proof Construction

## Story CLPR-8.3: Ethereum Proof Construction

**Parent Epic:** CLPR-8: Besu Endpoint
**Repo:** TBD

### Objective

`EthereumProofConstructor` reads ClprService contract state and constructs Merkle-Patricia trie proofs.

### Acceptance Criteria

- **AC-1:** Reads ClprService storage slots: queue metadata, message entries, connection state.
- **AC-2:** Constructs Merkle-Patricia trie proofs from state root to each storage slot.
- **AC-3:** Includes block header: number, state root, timestamp.
- **AC-4:** Commitment level configurable: `latest`, `safe`, `finalized`. Default `finalized`.
- **AC-5:** `SyncCommitteeTracker` maintains current Ethereum sync committee.
- **AC-6:** State reading: `BlockchainQueries` (in-process) > localhost JSON-RPC (fallback).
- **AC-7:** Caps messages at `max_messages_per_bundle`. Empty when no pending messages.

### Dependencies

- CLPR-8.1 (Besu service access)
- CLPR-6 (storage layout)

### Risk

**High** — Besu Plugin API may not expose world state trie access. May need upstream contribution. Merkle-Patricia proof construction non-trivial.