fix(docs): update native plugin reference links

[maho0638]

Summary

Updates the native AI agent plugin reference links to point to the current master branch in base/skills.

Why

The native plugin docs currently link to files under:

https://github.com/base/skills/blob/main/...

But base/skills uses master as its default branch, so those GitHub reference cards resolve to broken links.

Fixes #1531.

Verification

• Updated only files under docs/ai-agents/plugins/native
• Replaced the broken blob/main skill reference links with blob/master
• Verified the branch diff only touches the native plugin reference links

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/2	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2