Samle CSS i én delt fil og oppdater stempler

Flytt identisk style.css fra kalkulatorkatalogene til public/style.css
og oppdater alle index.html til å referere ../style.css.

Nye stempler: «Penger lager penger» (sparing), «Boligfesten» (bolig),
«Fødselsloteriet» (arv) + sarkastisk åpning i arv-banneret.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -8,13 +8,16 @@ Collection of interactive calculators visualizing how seemingly small difference
 
 ## Architecture
 
-Static site in `public/` — no build system, no package manager. Serve `public/` as the site root. Each topic gets its own subdirectory with `index.html`, `style.css`, `app.js`.
+Static site in `public/` — no build system, no package manager. Serve `public/` as the site root. Each topic gets its own subdirectory with `index.html` and `app.js`.
+
+### Shared CSS
+
+`public/style.css` — Shared stylesheet used by all calculators (referenced as `../style.css`). CSS custom properties in `:root`, CSS Grid layouts, responsive breakpoints at 560px/480px/360px. Calculators can add a supplementary `<style>` block or extra CSS file for page-specific styles if needed.
 
 ### Shared pattern (all calculators)
 
-Each calculator directory contains three files following the same pattern:
-- `index.html` — Header, range-slider controls, stat cards, chart canvases, explainer section
-- `style.css` — Identical copy across all calculators. CSS custom properties in `:root`, CSS Grid layouts, responsive breakpoints at 560px/480px/360px
+Each calculator directory contains two files following the same pattern:
+- `index.html` — Header, range-slider controls, stat cards, chart canvases, explainer section. Links to `../style.css`.
 - `app.js` — Self-contained logic with `fmtKr()`, `fmtShort()`, `getData()`, `baseOpts()`, `update()`. Charts update with `'none'` animation mode.
 
 ### Calculators