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>

nginx.conf

@@ -0,0 +1,46 @@
+worker_processes auto;
+
+events {
+    worker_connections 1024;
+}
+
+http {
+    include       /etc/nginx/mime.types;
+    default_type  application/octet-stream;
+
+    types {
+        application/wasm wasm;
+    }
+
+    sendfile    on;
+    tcp_nopush  on;
+    gzip        on;
+    gzip_types  text/plain text/css application/json application/javascript text/xml application/xml application/wasm;
+
+    server {
+        listen 80;
+        server_name _;
+        root /usr/share/nginx/html;
+        index index.html;
+
+        # Cache static assets
+        location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff2?|ttf|wasm)$ {
+            expires 30d;
+            add_header Cache-Control "public, immutable";
+        }
+
+        # Proxy /api/ requests to the backend
+        location /api/ {
+            proxy_pass http://backend:3001;
+            proxy_set_header Host $host;
+            proxy_set_header X-Real-IP $remote_addr;
+            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+            proxy_set_header X-Forwarded-Proto $scheme;
+        }
+
+        # SPA fallback — serve index.html for all other routes
+        location / {
+            try_files $uri $uri/ /index.html;
+        }
+    }
+}