Switch to master branch + Gitea Actions

- Move CI/release workflows from .github/workflows to .gitea/workflows (Gitea Actions),
  targeting the master branch.
- docker-publish: push to the Gitea container registry (git.finalfactory.de) with a
  lowercased image name; login via github.token or a PACKAGES_TOKEN secret.
- version-tag: gitea-actions bot identity; optional RELEASE_TOKEN to re-trigger the image build.
- Update README/CLAUDE.md/Unraid template/build-and-push.ps1 to the Gitea registry + master.

Claude-Session: https://claude.ai/code/session_01WujdMtMJPbxDpDnMeK22rr

.gitea/workflows/ci.yml

@@ -0,0 +1,29 @@
+# Gitea Actions: build + test on push/PR. Integration tests spin a TimescaleDB via Testcontainers,
+# so the act_runner label used here must be a Docker-capable runner (docker-in-docker or a host
+# runner with a reachable Docker socket).
+name: ci
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  build-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: "10.0.x"
+
+      - name: Restore
+        run: dotnet restore
+
+      - name: Build
+        run: dotnet build --no-restore -c Release
+
+      - name: Test
+        run: dotnet test --no-build -c Release --logger "trx;LogFileName=test-results.trx"