Promote the future-CSP constraint from an inline Caddyfile comment to a
durable ADR-028: serve the pdf.js wasm decoders same-origin (never a
CDN), any future CSP must allow 'wasm-unsafe-eval' + worker-src 'self'
blob:, and the build-time guard keeps the wasm shipping. Caddyfile now
points at the ADR.
Addresses re-review: Markus (constraint should be an ADR, not a comment).
Refs #708
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
