Redesign site and modernize tooling

Replace the HTML5-UP "Strata" theme with a Swiss-minimal single-page
design (plain CSS, Space Grotesk / Hanken Grotesk / Space Mono). Rewrite
copy for current positioning: Staff Data, Analytics & AI Engineer at
Swisscom, open to new work. Experience shown as a pipeline timeline;
contact simplified to email + LinkedIn (drop the broken form).

Prune unused deps (lightbox, FontAwesome, sass/gatsby-plugin-sass) and
the old SCSS, fonts and gallery assets. Fix package.json metadata.

Harden the Gitea deploy: merge build+deploy into one job (removes the
deprecated artifact upload/download handoff), bump Node 18 -> 20, use
npx gatsby build. Rename .nvrmc -> .nvmrc and refresh the README.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -1,18 +1,27 @@
-# gatsby-starter-strata
+# thiessen.io
 
-**This is a starter for Gatsby.js V2.**
+Personal site of **Dennis Thiessen** — Staff Data, Analytics & AI Engineer (Bern, Switzerland).
 
-**The older V1 version of this starter can be found on the v1 branch**
+Built with [Gatsby](https://www.gatsbyjs.com/) 5 and React 18. Single-page, Swiss-minimal design; styles are plain CSS in `src/assets/style.css` (no preprocessor).
 
-Gatsby starter based on the Strata site template, designed by [HTML5 UP](https://html5up.net/strata). Check out https://codebushi.com/gatsby-starters/ for more Gatsby starters and templates.
+## Develop
 
-## Preview
+```bash
+npm install --legacy-peer-deps
+npx gatsby develop      # http://localhost:8000
+```
 
-http://gatsby-strata.surge.sh/
+## Build
 
-## Installation
+```bash
+npx gatsby build        # output in ./public
+```
 
-Install this starter (assuming Gatsby is installed) by running from your CLI:
-`gatsby new gatsby-starter-strata https://github.com/ChangoMan/gatsby-starter-strata`
+Use Node 20 (see `.nvmrc`).
 
-Run `gatsby develop` in the terminal to start.
+## Deploy
+
+Pushing to `master` triggers the Gitea Actions workflow in
+`.gitea/workflows/workflow.yaml`, which builds the site and rsyncs `public/`
+to the web server over SSH. It relies on these repository secrets:
+`SSH_PRIVATE_KEY`, `SSH_KNOWN_HOSTS`, `DEPLOY_USER`, `DEPLOY_HOST`, `DEPLOY_PATH`.