Backend, sync, infra, docs: ETag, API versioning, k8s, web scaffold, Android 16, domain stubs

- Backend: ShallowEtagHeaderFilter for /api/v1/*, API-VERSIONING.md, README (tenant, CORS, Flyway, ETag)
- k8s: backend-deployment.yaml (Deployment, Service, Secret/ConfigMap)
- Web: scaffold with directory pull, 304 handling, touch-friendly UI
- Android 16: ANDROID-16-TARGET.md; BuildConfig STUN/signaling, SMOAApplication configures InfrastructureManager
- Domain: CertificateManager revocation stub, ReportService signReports, ZeroTrust/ThreatDetection minimal docs
- TODO.md and IMPLEMENTATION_STATUS.md updated; communications README for endpoint config

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/Dockerfile

@@ -0,0 +1,18 @@
+# Build from repo root: docker build -f backend/Dockerfile .
+FROM eclipse-temurin:17-jdk-alpine AS build
+WORKDIR /workspace
+
+COPY . .
+RUN ./gradlew :backend:bootJar --no-daemon -x test
+
+# Run stage
+FROM eclipse-temurin:17-jre-alpine
+WORKDIR /app
+
+RUN adduser -D -s /bin/sh appuser
+USER appuser
+
+COPY --from=build /workspace/backend/build/libs/*.jar app.jar
+
+EXPOSE 8080
+ENTRYPOINT ["java", "-jar", "app.jar"]