docs(tutorial): Stacking - Building a Decentralized Stacking Pool

[jadonamite]

Description
This PR adds Module 1: Stacking by @jadonamite. It documents the implementation of a decentralized stacking pool using the new pox-4 trait. It specifically addresses the transition from passive locking to active signer validation required for the Nakamoto release.

Content Overview
Concept: Explains the role of the Signer in PoX-4 reward distribution.

Implementation: Provides the pattern for stack-aggregation-commit-indexed with signer authorization.

Validation: Outlines how to verify signer-node event observation.

Checklist
[x] Content verified against Stacks Epoch 3.0 (Nakamoto).

[x] Code examples follow security best practices for signer signatures.

[x] Formatting follows the repository's Docusaurus style guide.

Related Issues
Closes # (If applicable)

[jadonamite]

@eric-stacks i hope this meets the requirement for tutorials i don't think it should be anywhere else , hopefully you review