Plugin system plus two base plugins

[agpituk]

Add Harbor Plugin System

This PR introduces a plugin architecture that allows separate Firefox extensions to provide tools to Harbor. Plugins communicate via extension-to-extension messaging (browser.runtime.sendMessage) and their tools are exposed to web applications through the existing window.agent API.

Documentation

• docs/plugins-quickstart.md - Get started with plugins in 5 minutes
• docs/plugin-protocol.md - Wire protocol specification
• docs/plugins-dev.md - Full plugin development reference

Summary

• Plugin system infrastructure - Registration, health checks, and tool routing between Harbor and plugin extensions
• Consent management - Per-origin permission control for plugin tools (Allow Once/Always/Deny)
• Two example plugins - harbor-plugin-time and harbor-plugin-decode demonstrating the protocol
• Full integration - Plugin tools work in both window.agent.tools.call() API and sidebar chat

Architecture

Web Page Harbor Hub Plugin Extension
(window.agent) ←→ (aggregates tools, ←→ (provides tools,
enforces consent) executes them)

Plugins register with Harbor on startup, and Harbor namespaces their tools as pluginId::toolName. Web pages see plugin tools alongside MCP tools with unified consent handling.

New Files

Path	Description
extension/src/plugins/	Plugin system (router, registry, consent, types)
plugins/harbor-plugin-time/	Time tools (time.now, time.format)
plugins/harbor-plugin-decode/	Decode tools (decode.base64_encode, decode.base64_decode, decode.json_pretty, decode.jwt_decode_unsafe)
docs/plugin-protocol.md	Wire protocol specification
docs/plugins-dev.md	Plugin development guide
docs/plugins-quickstart.md	Getting started guide

Next Steps

This plugin system lays the groundwork for making the native bridge optional. Since plugins run entirely in the browser and can make HTTP requests, a future "LLM plugin" could communicate directly with Ollama's HTTP API, enabling Harbor to function without the Node.js bridge for users who only need local LLM access.