Remove contract registry - moved to dedicated repository (#77)

* Remove contract registry - moved to dedicated repository

The contract registry functionality has been moved to a dedicated repository
at https://github.com/burnt-labs/deployed-contract-listings

This change:
- Removes contracts.json and related scripts
- Removes package.json dependencies used only for the registry
- Updates README with notice about the new location
- Keeps only the contract source code in this repository

The new dedicated repository provides:
- Interactive web interface with search and filtering
- Modern Xion Dashboard design system
- GitHub Pages deployment
- Better separation of concerns between contract code and registry

* Remove contract registry GitHub Actions workflows

Removes workflows that were specific to the contract registry:
- validate.yml: Used to validate contracts.json and README sync
- verify-contracts.yml: Used to verify deployed contracts daily

Keeps the essential workflows for contract development:
- Basic.yml: Rust test suite for contract compilation
- Release.yml: WASM release workflow for contract artifacts

* Replace contract registry PR template with contract development template

The old PR template was entirely focused on adding contracts to the registry.
This new template is appropriate for actual contract development PRs.

New template includes:
- Type of change (bug fix, feature, breaking change, etc.)
- Which contracts are affected (Account, Treasury, User Map)
- Testing checklist
- General development checklist

This aligns with the repository's new focus on contract source code
rather than the deployed contract registry.

* Remove PR template entirely

The PR template was specific to the contract registry.
Since the repository now focuses on contract source code,
a PR template is not necessary. Developers can provide
relevant context as needed for each PR.

Author: justinbarry