feat: Agent Logic Contract Examples with IAgentLogic Interface

[saiboyizhan]

Summary

Adds three example logic contracts demonstrating how to extend BAP-578 agents with custom on-chain capabilities via the logicAddress field.

Currently there are no examples showing developers how to build logic contracts for their agents. This PR fills that gap with practical, well-documented examples.

What's Included

Standard Interface

• IAgentLogic — A common interface (execute + description) that all logic contracts implement
• IBAP578 — Minimal read-only interface for verifying agent ownership and state

Example Contracts

Contract	Description
SimpleTrader	Token swap executor with per-trade (1 BNB) and daily (5 BNB) spend limits
PriceAlert	On-chain price monitoring using Binance Oracle with keeper-compatible alert checks
AutoFunder	Automatic agent balance top-up when funds drop below a configurable threshold

Documentation

• Full README with architecture diagram, quick-start guides for each contract, and a "Building Your Own Logic Contract" tutorial

File Structure

contracts/community/examples/
├── interfaces/
│   ├── IAgentLogic.sol
│   └── IBAP578.sol
├── SimpleTrader.sol
├── PriceAlert.sol
├── AutoFunder.sol
└── README.md

Key Design Decisions

• All contracts verify bap578.ownerOf(tokenId) == msg.sender before execution
• PriceAlert uses Binance Oracle Feed Adapters (native to BNB Chain)
• AutoFunder and PriceAlert are keeper-compatible (public check functions callable by anyone)
• Each contract includes clear warning that these are educational examples

Test Plan

• Hardhat compilation passes (0 errors, 0 warnings)
• Prettier formatting check passes
• All 31 existing tests still pass (no regressions)
• No conflicts with existing community contracts