chore: add SPDX copyright attribution and a NOTICE file

[re-gius]

Description

Aligns the repository with the legal guidelines for open source attribution.

• Every Parity-authored contract gains one line under its SPDX identifier: SPDX-FileCopyrightText: © 2026 Parity Technologies. A contract file travels alone through explorers and vendoring, and carried a license identifier with no copyright holder to preserve; SPDX-FileCopyrightText is the REUSE-standard field for this, so coverage stays machine-checkable.
• Vendored third-party code keeps its own notices: contracts/external/ (authoritative SPDX headers) and contracts/utils/Multicall3.sol (mds1/multicall3, MIT) carry no Parity line.
• A NOTICE file records the project copyright, the MIT license pointer, and the third-party attributions; the README's license section now points at it.

Comment-only for the contracts: bytecode, ABIs, and storage layouts are unchanged.

Type

• Bug fix
• Feature
• Breaking change
• Documentation
• Chore
• Refactor
• Security

Scope

• Registration
• Resolver
• Store
• Proof of Personhood
• Deployment scripts
• Tests

Related Issues

Fixes

Checklist

Code

• Follows project style
• forge build passes
• forge test passes
• No new compiler warnings

Testing

• New tests added for changed behavior
• Fuzz tests added where applicable
• Invariant tests verified

Security

• No new selfdestruct or delegatecall
• Access control reviewed
• No storage layout conflicts (for upgradeable contracts)

Documentation

• NatSpec updated on changed interfaces
• README updated if needed

Breaking Changes

• No breaking changes
• Breaking changes documented below

Breaking changes:

How to test

grep -rL "SPDX-FileCopyrightText" contracts --include='*.sol' | grep -v external

Prints only contracts/utils/Multicall3.sol, the vendored file that keeps its original authors' notice.

Notes

The added lines change each file's compiler metadata hash and nothing else. Release tooling strips metadata before comparing codehashes, so codehashes.json and the deployed-bytecode checks are unaffected.

[github-actions]

CI Summary

Check	Result
4naly3er Analysis	Found 38 issues: 5 medium, 8 low, 13 gas, 12 informational - View Report
Slither Analysis	Found 193 issues: 4 high, 40 medium, 90 low, 59 informational - View Report
Contract Tests (Unit + Fuzz)	All tests passed (681 total) - View Report
Contract Tests (Invariant)	All tests passed (58 total) - View Report
Gas Report	9 contracts analyzed - View Report
Coverage	Failed - Tests failed, cannot compute coverage
Documentation	Passed - 66 pages generated - View Docs
Format & Lint	Passed - Code formatted correctly
File Validation	Passed - All tracked files valid
Deploy Contracts	Reproduces the expected address set; resume verified
PR Title	PR Title Valid
Labels	Unknown
Secret Scan	Passed - No secrets detected