fix: accurate positioning — implement contracts, pin Hardhat, correct README

[Yudis-bit]

Summary

Reframes the project as a simulation prototype, implements the previously empty Solidity contracts, and pins Hardhat.

Changes

1. Implement empty Solidity contracts

• INodeRegistry.sol was 0 bytes → now contains a minimal interface with registerNode, stake, getTrustScore, isRegistered
• NodeRegistry.sol was 0 bytes → now contains a reference implementation with registration, staking, and trust score storage

2. Pin Hardhat toolchain

• package.json: Added hardhat ^2.22.0 and @nomicfoundation/hardhat-toolbox ^4.0.0 as devDependencies
• hardhat.config.js: Was 0 bytes → now contains minimal config with Solidity 0.8.20

3. Update README to accurately describe project scope

• Title changed from "Layer-0/Layer-1 enhancement protocol" to "Simulation Prototype"
• Phase 5 clarified as "reference interface and stub contract"
• The 23.8% delivery ratio and survivorship bias are already documented in the README (line 16)

4. Repo description updated

• Removed "faster, smarter, and harder to break"
• Now reads: "Seeded Python simulation exploring adaptive routing with Multi-Armed Bandit RL"

Test Results

All 6 smoke tests pass:

test_baseline_finds_west_to_east_route ... ok
test_cognitive_router_avoids_congested_link ... ok
test_cognitive_router_delivers_some_packets ... ok
test_cognitive_router_reports_latency_gain ... ok
test_dumb_router_delivers_all_packets ... ok
test_simulation_completes ... ok