feat: complete phase 5 -- error hardening, frontend, Docker, demo, docs

Backend:
- ConversationTracker: Protocol + PostgresConversationTracker for lifecycle tracking
- Error handler: ErrorCategory enum, classify_error(), with_retry() exponential backoff
- Wire PostgresAnalyticsRecorder + ConversationTracker into ws_handler
- Rate limiting (10 msg/10s per thread), edge case hardening
- Health endpoint GET /api/health, version 0.5.0
- Demo seed data script + sample OpenAPI spec

Frontend (all new):
- React Router with NavBar (Chat / Replay / Dashboard / Review)
- ReplayListPage + ReplayPage with ReplayTimeline component
- DashboardPage with MetricCard, range selector, zero-state
- ReviewPage for OpenAPI classification review
- ErrorBanner for WebSocket disconnect handling
- API client (api.ts) with typed fetch wrappers

Infrastructure:
- Frontend Dockerfile (multi-stage node -> nginx)
- nginx.conf with SPA routing + API/WS proxy
- docker-compose.yml with frontend service + healthchecks
- .env.example files (root + backend)

Documentation:
- README.md with quick start and architecture
- Agent configuration guide
- OpenAPI import guide
- Deployment guide
- Demo script

48 new tests, 449 total passing, 92.87% coverage

.env.example

@@ -0,0 +1,25 @@
+# Smart Support -- Docker Compose environment variables
+# Copy to .env and fill in your values
+
+# PostgreSQL password (used by both postgres and backend services)
+POSTGRES_PASSWORD=dev_password
+
+# LLM provider: anthropic | openai | google
+LLM_PROVIDER=anthropic
+LLM_MODEL=claude-sonnet-4-6
+
+# API keys (provide the one matching LLM_PROVIDER)
+ANTHROPIC_API_KEY=
+OPENAI_API_KEY=
+GOOGLE_API_KEY=
+
+# Optional: webhook URL for escalation notifications
+WEBHOOK_URL=
+
+# Session and interrupt TTL in minutes
+SESSION_TTL_MINUTES=30
+INTERRUPT_TTL_MINUTES=30
+
+# Optional: load a named agent template instead of agents.yaml
+# Available templates: ecommerce, saas, generic
+TEMPLATE_NAME=