Example and Tutorial for end to end signature flow - for intent based applications.

### Feature description

A complete, canonical example of the signature flow.

The goal of this tutorial should be to provide a complete, executable example that can be followed by a third-party developer from start to finish.

## Scope

- Message construction.
- Message serialization.
- Message hashing.
- Signature generation:
- in the frontend / wallet.
- in rust client
- Signature transport and submission.
- Signature verification
- in rust client
- inside the vm.
- Handling invalid signatures.
- Using successful verification to authorize an action.

## Requirements
### Canonical Message Format

Provide a simple but realistic message structure that can be used throughout the tutorial.

The purpose is not to define a standard intent format, but to establish a reproducible example for demonstrating signing and verification.

The exact fields are less important than ensuring the entire flow is deterministic and reproducible.

### Canonical Serialization Format

Explicitly define:

- field ordering
- encoding format
- integer representation
- byte ordering
- array handling
- serialization boundaries

### Message Hashing

Demonstrate:

- how the message is transformed into a signing payload
- which hash function is used
- how the digest is represented
- how the digest is passed into signing and verification logic

The exact intermediate values should be shown.

### Frontend Signing Example

Provide a complete frontend example showing:

- message construction
- serialization
- hashing
- signature generation
- extraction of the public key
- resulting signature output

The example should be executable with minimal modification.

## Contract Verification Example

Provide a complete MASM example showing:

- receiving a message or digest
- receiving a signature
- receiving a public key
- performing signature verification
- handling success and failure cases
- execute a simple action based on message content

The example should compile and execute without modification.

End-to-End Integration Test

Provide a runnable integration example demonstrating:

- Construct message.
- Serialize message.
- Hash message.
- Sign message.
- Submit signature and payload.
- Verify signature inside a contract.
- Execute an authorized action.

The entire flow should be executable by a third-party developer without requiring protocol-level knowledge.

Security Considerations

The tutorial should explain:

- what exactly is being signed
- replay risks
- message uniqueness requirements
- recommended signing patterns
- common implementation mistakes

The tutorial should serve as the canonical reference for signature-based authorization on Miden.

### Why is this feature needed?

Currently, there is no end-to-end reference showing such a flow would be implemented in a realistic application.