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>

crates/mass-driver-backend/Cargo.toml

@@ -4,13 +4,13 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
-orbital-mechanics = { path = "../orbital-mechanics" }
-mass-driver-core = { path = "../mass-driver-core" }
 axum = "0.8"
 tokio = { version = "1", features = ["full"] }
-sqlx = { version = "0.8", features = ["runtime-tokio", "postgres"] }
+sqlx = { version = "0.8", features = ["runtime-tokio", "postgres", "chrono"] }
 serde = { workspace = true }
 serde_json = { workspace = true }
 tower-http = { version = "0.6", features = ["cors", "compression-gzip"] }
 tracing = "0.1"
 tracing-subscriber = "0.3"
+base64 = "0.22"
+chrono = { version = "0.4", features = ["serde"] }