Add co-president letterhead PDF exports

[AlaqmarG]

Description

• New Exports tile, co-presidents only (approverOnly + requireApprover on every route). PDFs on the club letterhead are built on demand and never stored. Downloads are rate limited and sent with no-store.
• Access Request: every current exec's name, student ID and access card ID. Anyone missing any of the three is left out of the PDF; the page lists who was skipped and what's missing, never the PDF.
• Access Removal: former execs from a past term whose card access should be revoked.
• Executive Roster: position, name, student ID, personal and club email. For student-union club registration and handover.
• Confirmation of Officers: positions and terms with co-president signature lines. For the credit union or the university.
• Events Report: events in a date range, with recurring series listed once.
• Signing Register: signing requests in a date range, with envelope, signers, status and dates.
• Unicode-safe (Noto Sans), tables repeat their header across pages, footer shows page X of Y, and exports containing personal information carry a Confidential marker.
• The letterhead header now lives in lib/documents/letterhead.ts, shared with the templates. The template PDFs are byte-identical after the refactor.

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
• 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 (light theme): every export downloads a valid PDF, a bad date range returns 400, an unknown export returns 404
• No secrets, internal hostnames or IPs committed

Testing Evidence

Exports page on the preview (names blurred)	Roster, officers, events and signing cards

• Signing Register shows 0 on previews because previews don't copy signing requests from prod.

Samples below are rendered from fake data through the real report code.

Access Request	Access Removal	Executive Roster
Confirmation of Officers	Events Report	Signing Register

The Access Request sample includes a fake exec missing an access card. They're left out of the table and the signature names; only the Exports page names them.