Refactor to static markdown (remove Supabase backend) + self-host build

Posts now read from data/posts/*.md via gray-matter + remark; authors derived
from posts. Removes admin dashboard, comments, subscriptions, and all Supabase
usage. Adds Dockerfile (Next.js standalone) + Gitea Actions CI. output: standalone.

.gitea/workflows/deploy.yml

@@ -0,0 +1,16 @@
+name: build-and-publish
+on:
+  push:
+    branches: [master, main]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Log in to the Gitea registry
+        run: echo "${{ secrets.REGISTRY_TOKEN }}" | docker login git.thebennett.net -u "${{ secrets.REGISTRY_USER }}" --password-stdin
+      - name: Build + push
+        run: |
+          docker build -t git.thebennett.net/reformedwitness/confessions-of-grace:latest -t git.thebennett.net/reformedwitness/confessions-of-grace:${{ github.sha }} .
+          docker push git.thebennett.net/reformedwitness/confessions-of-grace:latest
+          docker push git.thebennett.net/reformedwitness/confessions-of-grace:${{ github.sha }}