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>

docker-compose.yml

@@ -0,0 +1,28 @@
+version: "3.9"
+
+services:
+  postgres:
+    image: postgres:16-alpine
+    environment:
+      POSTGRES_USER: massdriver
+      POSTGRES_PASSWORD: massdriver
+      POSTGRES_DB: massdriver
+    ports:
+      - "5432:5432"
+    volumes:
+      - pgdata:/var/lib/postgresql/data
+
+  backend:
+    build:
+      context: .
+      dockerfile: Dockerfile.backend
+    ports:
+      - "3001:3001"
+    environment:
+      DATABASE_URL: postgres://massdriver:massdriver@postgres:5432/massdriver
+      PORT: "3001"
+    depends_on:
+      - postgres
+
+volumes:
+  pgdata: