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>

package.json

@@ -1,22 +1,16 @@
 {
-  "name": "gatsby-starter-default",
-  "description": "Gatsby default starter",
+  "name": "thiessen-io",
+  "description": "Personal site of Dennis Thiessen — thiessen.io",
   "version": "1.0.0",
-  "author": "Hunter Chang",
+  "author": "Dennis Thiessen",
   "dependencies": {
     "gatsby": "^5.12.12",
     "gatsby-plugin-manifest": "^5.12.3",
     "gatsby-plugin-offline": "^6.12.3",
     "gatsby-plugin-react-helmet": "^6.12.0",
-    "gatsby-plugin-sass": "^6.12.3",
-    "sass": "^1.69.5",
     "react": "^18.2.0",
     "react-dom": "^18.2.0",
     "react-helmet": "^6.1.0",
-    "yet-another-react-lightbox": "^3.15.6",
-    "@fortawesome/fontawesome-svg-core": "^6.5.1",
-    "@fortawesome/free-solid-svg-icons": "^6.5.1",
-    "@fortawesome/react-fontawesome": "^0.2.0",
     "ajv": "^8.12.0",
     "ajv-keywords": "^5.1.0",
     "schema-utils": "^4.2.0"