feat(projects): add playground architecture diagram and notes

Update the Playground entry on the projects page: diagram,
prerender, privacy and operations bullets, one challenge,
one learning, and the Traefik, nginx and Tailscale technologies.

src/assets/i18n/en.json

@@ -310,16 +310,19 @@
     "PLAYGROUND": {
       "TITLE": "Playground",
       "SHORT_DESCRIPTION": "This site: a portfolio with algorithm visualizations that run in the browser, some of them on the GPU.",
-      "INTRODUCTION": "This site is where I try things out. I wanted to see how far a plain browser gets with the algorithms I like, so every visualization runs on the client: pathfinding, maze generation, sorting, Conway's Game of Life, fractals in GLSL shaders, and two physics simulations that run as compute shaders on WebGPU. The rest is a normal Angular app with German and English texts, a dark mode, and a CI pipeline that builds and tests it and pushes it as a Docker image to my own registry.",
+      "INTRODUCTION": "This site is where I try things out. I wanted to see how far a plain browser gets with the algorithms I like, so every visualization runs on the client: pathfinding, maze generation, sorting, Conway's Game of Life, fractals in GLSL shaders, and two physics simulations that run as compute shaders on WebGPU. The rest is a normal Angular app with German and English texts, a dark mode, and a pipeline that takes every push to main all the way to the live server.",
       "BULLET_1": "Pathfinding with Dijkstra and A*, maze generation with Prim and Kruskal, five sorting algorithms with sound, Conway's Game of Life and a four-color map.",
       "BULLET_2": "2D fractals (Mandelbrot, Julia, Burning Ship, Newton) in one GLSL shader, and 3D fractals (Mandelbulb, Mandelbox, Julia-Bulb) by raymarching with normals from the distance field.",
       "BULLET_3": "A double pendulum and a cloth simulation run as compute shaders on WebGPU. Without WebGPU they fall back to the CPU or WebGL and say so in a snackbar.",
-      "BULLET_4": "Angular with Material and Tailwind, signals for state, German and English, and a service worker (PWA).",
-      "BULLET_5": "CI on Gitea Actions: lint, i18n check, tests, production build and a Lighthouse report. On main it builds a Docker image and pushes it to my own registry.",
+      "BULLET_4": "Angular with Material and Tailwind, signals for state, German and English. Every route is prerendered at build time into its own HTML with its own title and meta tags, so a shared link gets a proper preview. In the browser, Angular and a service worker (PWA) take over from the static page.",
+      "BULLET_5": "Privacy by design: the fonts come from the site itself, there are no cookies, no tracking and no access log on the server. Only language and theme are kept in the browser's local storage.",
+      "BULLET_6": "Operations: CI on Gitea Actions on my home server Tribble runs lint, i18n check, tests, the production build, a prerender check and Lighthouse. A push to main builds a Docker image; on the VPS, Watchtower pulls it, nginx serves the static files and Traefik handles HTTPS. Gitea itself is reached through Traefik over Tailscale.",
       "CHALLENGE_1": "The cloth solver on the GPU. XPBD constraints that share a particle cannot be solved in parallel without a race. I group the constraints by graph coloring into eight phases, so inside one phase no two constraints touch the same particle and each phase runs fully in parallel.",
       "CHALLENGE_2": "Not every browser has WebGPU. Both simulations have a CPU or WebGL path and a snackbar that says the fallback is active, so the page works everywhere and nobody wonders why it is slower.",
+      "CHALLENGE_3": "Prerendering a SPA that already existed. At build time every page is rendered in Node, and there is no WebGPU, no canvas for Babylon.js and no localStorage there. Browser-only code had to be guarded component by component until the build ran through. The client-side shell index.csr.html stays, because the service worker and the 404 page still need it.",
       "LEARNING_1": "Compute shaders change how you think about an algorithm. The data layout and the order of writes matter more than the math.",
-      "LEARNING_2": "A small CI with a key-parity check and a Lighthouse run catches the boring mistakes, a missing translation or a slow page, before I see them on the live site."
+      "LEARNING_2": "A small CI with a key-parity check and a Lighthouse run catches the boring mistakes, a missing translation or a slow page, before I see them on the live site.",
+      "LEARNING_3": "A privacy page is a spec for the server. Once it says there is no access log and no connection to Google, nginx must keep no log and the fonts must ship with the site. Writing it down first made those decisions for me."
     },
     "TRIBBLE": {
       "TITLE": "Self-Hosted Infrastructure",