docs: add mixed marketplace skills guide

[neubig]

Summary

Add documentation for the new mixed marketplace skills example that demonstrates how to combine local skills with remote skills from the OpenHands extensions repository.

Related PRs

• feat(examples): add mixed marketplace skills example software-agent-sdk#2299 - Example implementation
• feat: add configurable marketplace_path setting for public skills loading software-agent-sdk#2253 - marketplace_path feature

Changes

• New guide: sdk/guides/mixed-marketplace-skills.mdx

Content

The guide covers:

• Use case explanation: Why teams need mixed skill sources
• Loading pattern comparison: Table comparing load_skills_from_dir(), load_public_skills(), and load_available_skills()
• Full example: Embedded code from examples/01_standalone_sdk/43_mixed_marketplace_skills/main.py
• Local skill creation: How to create SKILL.md files
• Precedence rules: How local skills override public skills

Preview

The documentation explains:

1. Loading local skills from a project directory
2. Loading remote skills from OpenHands/extensions
3. Combining both with proper precedence handling
4. Using the combined skills with an agent

[enyst]

This reads like the marketplace defines local skills directly, but in OpenHands we're using the Claude Code plugin marketplace schema as a filter list for which public skills to load. Could we clarify that the marketplace entries are plugin names used as a filter, while local skills are merged separately?

Suggested change

	The marketplace.json can define:
	- Local skills to include
	- Remote skills to pull from OpenHands/extensions
	- Skill dependencies between local and remote skills
	The marketplace.json follows the Claude Code plugin marketplace schema. In OpenHands, the
	plugin entry names are used as a filter list for which public skills to load; local
	skills live in local_skills/ and are merged separately.

[enyst]

(HUMAN: this wasn't me - and I read it twice to make sure 😅 ... not fully sure when the agent reviewed this docs/ PR 😇 )

[enyst]

Reviewed latest changes. I left one inline suggestion to clarify that OpenHands uses the Claude Code plugin marketplace schema as a filter list for public skills, while local skills are merged separately. Otherwise LGTM.

[enyst]

OpenHands-GPT-5.2 here. I pushed a docs update clarifying that marketplace.json uses the Claude plugin schema plus the OpenHands skills[] extension, and that marketplace entries point to skill directories while local skills are merged separately. Commit: 32e23db.