Let executives hold multiple terms

[AlaqmarG]

Description

Stacked on #134 (Exports) — targets that branch, not main.

• Execs can now serve multiple terms. Term is a chip list (add/remove) instead of one dropdown, on both the co-president tile editor and an exec's own profile.
• A current exec with no term gets the current academic year assigned automatically — once at startup for existing tiles, and immediately whenever a tile becomes current (approval, creation, returning to the team).
• Everywhere a term is shown (team page, Users, admin search, exports) now shows the exec's newest term.
• Team page: a returning exec appears once, under their newest term; their alumni card lists every year they served; search matches any of them.
• Access Removal (Exports) now catches anyone who served in the chosen year, not just those whose newest term is that year.
• Fixes a false "this document isn't for the current year" warning on exports between April and August, when the incoming team's tiles legitimately carry next year already.

Checklist

• npm run typecheck, npm run lint, npm run format:check and npm run build pass
• Schema changes have a committed migration (npm run db:generate) — none (jsonb)
• New env vars added to .env.example, .env.local.example, deploy/docker-compose.yml and komodo/deploy-context.mjs — none
• Admin-only routes gated with requireAdmin / requireApprover
• Tested on the branch's preview deploy: public team page (light theme). Admin-side chip editor and palette hint need a sign-in to click through.
• No secrets, internal hostnames or IPs committed

Testing Evidence

• No current exec or alumnus in the copied prod data serves more than one term yet, so the "Also served" line and multi-term chip editor aren't visible against real data here — they're covered by the workflow's fake-data behaviour script (19/19 checks) instead.