#945 Add associative info to user profiles: collective membership + collaborative contributions

Problem

The user profile (e.g. /u/webframp) is a strong record of what a person did alone: the CLI-usage sunburst, published extensions, writings, tier, streak, and badges. What it does not show is the associative layer — who a person is connected to and what they built with others.

Today a visitor cannot tell:

• which collectives a user belongs to, and
• what collaborative artifacts they produced — merged issues, shipped fixes, and similar contributions that landed in someone else's or a collective's work.

The profile should do double duty: prove contribution (credibility) and convey level of engagement and standing.

Proposed solution

Add an associative section to the profile that surfaces:

1. Collectives the user belongs to (collectives are explicit orgs/teams you join). Public collectives always show; private collectives appear only when the user opts in to reveal them on their profile.
2. Collaborative contributions — merged issues and shipped fixes — presented as a scannable, linkable record.

Preferred presentation (open to iteration): a collective-anchored view where each collective the user belongs to expands to show the contributions shipped under it, with one compact relational visualization the visitor can click into to explore connections. This matches the existing click-into-detail feel of the points sunburst without resorting to a hard-to-read network graph.

Points are out of scope. Points continue to display as they do today and stay earned separately by actual events and activity; this feature does not tie the associative data to scoring.

Alternatives considered

• Flat sections — two new card lists (Collectives, Shipped Contributions) mirroring the existing Extensions and Writings sections. Simplest and most consistent, but the least associative.
• Relational constellation — a full network graph centering the user, with clickable collective/collaborator/artifact nodes. Most visual, but graphs are hard to keep readable and risk feeling flashy over useful.

Related

• #933 — "Add a 'my collective extensions' filter to extensions page" (adjacent collective-surfacing work, different surface).