ci) add gitea actions and refresh readme (#1)

Summary:\n- replace scaffold README with project-specific setup, testing, Docker, and CI docs\n- add PR workflow to run lint, unit tests, app build, and Docker build\n- add main-branch workflow to build and push Docker images to Gitea registry\n\nNotes:\n- publish workflow expects REGISTRY_USERNAME and REGISTRY_PASSWORD repository secrets\n- image tags pushed: latest and short commit SHA\n\nTesting:\n- not run locally (workflows execute in Gitea Actions)
Reviewed-on: CampbellWireless/trips#1
Co-authored-by: Shaun Campbell <shaun@campbellwireless.net>
Co-committed-by: Shaun Campbell <shaun@campbellwireless.net>

.gitea/workflows/main-image.yml

@@ -0,0 +1,52 @@
+name: Build and Push Image
+
+on:
+  push:
+    branches:
+      - main
+
+env:
+  REGISTRY_HOST: git.campbellwireless.net
+  IMAGE_NAME: ${{ github.repository }}
+
+jobs:
+  docker-build-and-push:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        env:
+          REPO_URL: https://cloud.campbellwireless.net/git/${{ github.repository }}.git
+        run: |
+          set -eux
+          git init .
+          git remote add origin "$REPO_URL"
+          auth="$(printf '%s' '${{ github.actor }}:${{ secrets.GITHUB_TOKEN }}' | base64 | tr -d '\n')"
+          git config --local http.https://cloud.campbellwireless.net/.extraheader "AUTHORIZATION: basic $auth"
+          git fetch --prune --no-recurse-submodules origin +refs/heads/*:refs/remotes/origin/* +refs/tags/*:refs/tags/*
+          git checkout --detach "${{ github.sha }}"
+
+      - name: Setup Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Gitea registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY_HOST }}
+          username: ${{ secrets.REGISTRY_USERNAME }}
+          password: ${{ secrets.REGISTRY_PASSWORD }}
+
+      - name: Compute image tags
+        id: tags
+        run: |
+          echo "sha_short=$(echo '${{ github.sha }}' | cut -c1-12)" >> "$GITHUB_OUTPUT"
+
+      - name: Build and push image
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: ./Dockerfile
+          push: true
+          tags: |
+            ${{ env.REGISTRY_HOST }}/${{ env.IMAGE_NAME }}:latest
+            ${{ env.REGISTRY_HOST }}/${{ env.IMAGE_NAME }}:${{ steps.tags.outputs.sha_short }}