Typesafe, single-source-of-truth SSR/SSG pipeline

Combining some related issues concerning the design of our SSR pipeline to make a single branch and !MR. I hope this will be relatively easy to review.

1. Type safety throughout the build pipelines to enable autocomplete and to prevent obscure errors
2. Cohesion within .ts modules for easier maintenance, features and refactors
3. Consistency of styles and patterns
4. Single-source-of-truth principle so we can understand where effects originate

• #99 (closed) Use typesafe typescript libraries to model invariants and enforce narrow constraints

-> Typesafe functions to prevent undebuggable build-time errors

• #104 (closed) Migrate from separate scss files to narrow tokens in a typesafe css.ts module

-> Typesafe css builder -> Cohesion (less indirection, more inlining)

• #102 (closed) Query the CMS for design tokens and derive all metrics (Spacing & Colors) from CMS

-> Consistent and typesafe colors and spacings -> Singe source of truth

• #96 (closed) Fix the fluid scale: Less size contrast on small screens; get grid metrics from CMS

-> Consistent and typesafe widths and heights -> Singe source of truth

Also included in this branch: #103 (closed) Fix

element for correct Html output