feat: add Honcho conversational memory integration example

[alogotron]

Summary

Adds a complete Honcho conversational memory integration as an example user extension, demonstrating persistent user context across Agent Zero sessions.

Closes #1054

What is Honcho?

Honcho is a conversational memory platform by Plastic Labs that provides persistent user context across sessions — enabling agents to remember user preferences, past interactions, and build ongoing relationships.

Changes

All files are added under agents/_example/extensions/ as a reference implementation:

File	Extension Hook	Purpose
honcho_helper.py	Core module	Client management, message sync, context retrieval, caching
agent_init/_20_honcho_init.py	agent_init	Lazy session initialization on agent start
hist_add_before/_20_honcho_sync.py	hist_add_before	Real-time message sync to Honcho
system_prompt/_30_honcho_context.py	system_prompt	Inject persistent user context into prompts
README_HONCHO.md	Documentation	Setup instructions, architecture, usage guide

Key Features

• Lazy initialization — no restart needed; activates when API key is set in Secrets
• Automatic message sync — every message flows to Honcho via hist_add_before hook
• Context injection — user memory from past sessions injected into system prompt
• TTL-based context caching (120s) — prevents excessive API calls
• Graceful degradation — silently skips if unconfigured or SDK missing
• Zero config — only requires HONCHO_API_KEY in A0 Secrets

Data Flow

User message  → hist_add_before hook → sync to Honcho
Agent response → hist_add_before hook → sync to Honcho
New session   → system_prompt hook   → fetch & inject user context

Requirements

• honcho-ai>=2.0 (pip install honcho-ai)
• Honcho API key from app.honcho.dev

Relation to #998 (Unified Plugin System)

This integration is designed to work with the current extension system and is ready to be adapted to the plugin architecture proposed in #998 once it lands.

Testing

• All Python files compile without errors
• Tested on Agent Zero v0.9.8 with Honcho SDK v2.0.1
• Uses standard A0 extension hooks (agent_init, hist_add_before, system_prompt)
• No modifications to core A0 code