docs(wp-interactivity-api): Add WordPress 6.9 client navigation requirements

[derintolu]

Summary

Adds documentation for the WordPress 6.9 requirement that script modules must be explicitly marked as compatible with client-side navigation.

Per Interactivity API's client navigation improvements in WordPress 6.9:

For other script modules registered "manually", developers must use the add_client_navigation_support_to_script_module method of the main WP_Interactivity_API instance.

Without this, the router will not intercept link clicks on pages using manually registered script modules.

Changes

• SKILL.md: Updated client-side navigation section with WP 6.9+ requirements
• references/router.md: Added new reference document with full router documentation

Key Addition

// Mark module as compatible with client-side navigation (WordPress 6.9+ REQUIRED)
wp_interactivity()->add_client_navigation_support_to_script_module('my-navigation');

For blocks, use block.json:

{
  "supports": {
    "interactivity": { "clientNavigation": true }
  }
}

Test Plan

• Verified this requirement on a production WordPress 6.9 site
• Confirmed router does not intercept links without this call
• Confirmed router works correctly after adding this call

🤖 Generated with Claude Code

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Co-authored-by: derintolu <derintolu@git.wordpress.org>

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[justlevine]

TBF this could be asked about all of the existing committed skills, but what's the point of dumping all this information here if it's available via references?

[justlevine]

We should avoid yelling out our models since this needs to service more than just Anthropic