#933 Add a 'my collective extensions' filter to extensions page

Problem

On https://swamp-club.com/extensions, users who publish extensions under a collective or profile currently need to type one or more namespace/profile names into search to find their own extensions. This is cumbersome when a user belongs to a collective or publishes under multiple names, especially as the number of extensions grows.

Proposed solution

Add a filter on the extensions page to show all extensions owned by the signed-in user and their collective(s) without requiring the user to manually type each namespace/profile name.

Possible UI labels:

• "My extensions"
• "My collective extensions"
• "Owned by me / my collectives"

Desired behavior

When enabled, the filter should include extensions published by:

• the signed-in user
• collectives/organizations the user belongs to or can publish under

This should work as a quick toggle/filter alongside the existing search/filter controls.

Alternatives considered

Continue typing every relevant namespace/profile name manually in the search box, but this does not scale and is easy to forget when the user has N names or collectives.