feat: Modernize plugin entry compatibility

[lan17]

Summary

This updates the plugin entry wiring to prefer OpenClaw's modern definePluginEntry(...) descriptor when the host SDK exposes it, while preserving compatibility with older gateways that still expect a raw register(api) export.

What changed

• added a dedicated src/plugin-entry.ts wrapper that probes for definePluginEntry
• fall back to the legacy register-function export when the helper is unavailable
• pointed index.ts at the new wrapper entrypoint
• added a local type shim for openclaw/plugin-sdk/plugin-entry
• added tests covering modern helper, migration-window fallback, and legacy fallback behavior
• documented the compatibility behavior in the README

Why

Newer OpenClaw versions surface a compatibility advisory for hook-only plugins that have not adopted the newer plugin entry shape. This change modernizes the package entry without changing plugin behavior or dropping support for older OpenClaw runtimes.

Impact

• newer gateways can load the package through the modern plugin entry helper when available
• older gateways continue to load the plugin through the existing raw register export path
• runtime Agent Control behavior is unchanged

Validation

• npm run lint
• npm run typecheck
• npm test

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/plugin-entry.ts	92.85%	0 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!