feat(badges): plumb working group and refined conference role badges

Summary

Phase 2 of the badge expansion. Wire `computeBadges` to consume tables that already exist in the schema but don't yet feed the recognition system: `group_memberships`, `event_committee_assignments`, `event_sessions`, and `event_session_types`. Adds ~10 new badges spanning sustained community participation and granular conference roles.

Requirements

• Working Group Member / Working Group Chair badges from `group_memberships` joined to `groups` (filter to working-group type, distinguish chair/co-chair from rank-and-file).
• Affinity Group Member / Affinity Group Coordinator from the same tables filtered to affinity-group type.
• Program Committee badge from `event_committee_assignments`.
• Reviewer badge from `event_committee_assignments` filtered to reviewer-style areas.
• Refined conference-role badges using `event_sessions` and `event_session_types`: Keynote Speaker, Plenary Speaker, Lightning Talk, Tutorial Lead, Workshop Lead, Birds of a Feather Lead, Panelist. Replaces the current heuristic regex on `event_attendances.notes` with a proper join.
• Backwards compatibility: existing `Talk` and `Poster` badges continue to work for events that don't have richer session data.
• `pickFeaturedBadges` updated — Keynote and Plenary should rank near the top of the achievements strip alongside Service tier.

Context

Tables already exist (verified during the disciplines/skills work): `groups`, `group_memberships`, `event_committee_areas`, `event_committee_assignments`, `event_sessions`, `event_session_presenters`, `event_session_types`. Nothing in `badges.ts` reads them today.

The Phase 1 issue (#1951) is a prerequisite — its widened `computeBadges` signature is the natural place to add these new inputs. Phase 3 introduces the brand-new `awards` / `mentorship` / `contributions` tables.

Implementation Notes

• `loadMemberDossier` will need to load these additional rows (or join them lazily) before passing to `computeBadges`. Worth measuring query count — the Promise.all batch is already a few queries deep.
• Conference-role badges should prefer `event_sessions` data over `event_attendances.notes` regex. If a session matches via `event_session_presenters`, emit the session-type badge; otherwise fall back to the existing logic.
• Group membership end-dating (if the join carries dates) should distinguish "current chair" from "former chair" — current rates higher in the visual hierarchy.

Start with Phase 1 issue #1951, then inspect badges.ts and loadMemberDossier to trace how computeBadges receives data. Load the named group, committee, session, and session-type rows, implement the listed badges and ranking changes, preserve the existing Talk and Poster fallback, and measure the added query count.