Add Axum backend, Dockerfiles, and K8s deployment manifests

- Axum backend server: health check, transfer matrix cache (base64 BYTEA),
  route cache (JSONB), CORS, gzip compression, tracing
- Postgres schema: transfer_matrices + cached_routes tables with upserts
- Dockerfile.frontend: 3-stage (wasm-pack → SvelteKit → nginx:alpine)
- Dockerfile.backend: 2-stage (rust build → debian:bookworm-slim)
- nginx.conf: SPA fallback, WASM mime type, /api proxy to backend
- docker-compose.yml: Postgres + backend for local development
- K8s manifests: namespace, frontend/backend deployments with services,
  ingress routing, health probes, secret-based DATABASE_URL

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Dockerfile.backend

@@ -0,0 +1,14 @@
+# Stage 1: Build the backend binary
+FROM rust:1.82-slim AS builder
+RUN apt-get update && apt-get install -y pkg-config libssl-dev && rm -rf /var/lib/apt/lists/*
+WORKDIR /app
+COPY Cargo.toml Cargo.lock ./
+COPY crates/ crates/
+RUN cargo build --release --bin mass-driver-backend
+
+# Stage 2: Minimal runtime image
+FROM debian:bookworm-slim
+RUN apt-get update && apt-get install -y ca-certificates && rm -rf /var/lib/apt/lists/*
+COPY --from=builder /app/target/release/mass-driver-backend /usr/local/bin/mass-driver-backend
+EXPOSE 3001
+CMD ["mass-driver-backend"]