feat(hardening): M-Hard 6 + 7 — PostgreSQL backend + production server infra

M-Hard 6: PostgreSQL Storage Backend
- @shade/storage-postgres with PostgresStorage + PostgresPrekeyStore
- Drizzle-style raw SQL ensureClientTables / ensurePrekeyServerTables
- All tables prefixed `shade_` to avoid collisions in shared databases
- DELETE ... FOR UPDATE SKIP LOCKED for concurrent OTPK consumption
- Tests skip gracefully without SHADE_TEST_PG_URL, run against real PG when set

M-Hard 7: Production Server Infrastructure
- Structured JSON logger (logger.ts) — SHADE_LOG_LEVEL configurable
- Health endpoints (/health, /healthz, /ready) — Kubernetes-friendly
- Prometheus metrics (/metrics) — counters, histograms, middleware
- Graceful shutdown with SIGTERM/SIGINT handlers + store close
- Production Dockerfile with non-root user, healthcheck, multi-stage build
- docker-compose.yml example for Dokploy with optional PostgreSQL

193 tests passing, 0 failures.

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

packages/shade-server/.dockerignore

@@ -0,0 +1,7 @@
+node_modules
+dist
+*.tsbuildinfo
+.git
+.DS_Store
+**/tests
+**/*.test.ts