Add docker-compose, README, fix SSE dispatch

Use Undertow dispatch for SSE handler to avoid Ring adapter conflict.
Add docker-compose.yml (port 4101 to coexist with local dev on 4100).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

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+# btcdata
+
+Bitcoin data backend service. Fetches BTC prices from Binance (WebSocket) and Kraken (HTTP polling), stores them in PostgreSQL, and exposes a JSON API with Server-Sent Events for live price streaming.
+
+## API
+
+| Endpoint | Description |
+|---|---|
+| `GET /api/price/stream` | SSE stream — emits `price-update` events with JSON `{price, prev_price, recorded_at}` |
+| `GET /api/price/latest` | Latest price as JSON |
+| `GET /api/health` | Health check |
+
+## Quick Start
+
+```bash
+# Local dev (requires PostgreSQL)
+cp .env.example .env   # edit JDBC_URL
+make run               # starts on port 4100
+
+# Docker
+docker compose up -d   # starts on port 4101
+```
+
+## Environment Variables
+
+| Variable | Default | Description |
+|---|---|---|
+| `BTCDATA_PORT` | `4100` | HTTP server port |
+| `JDBC_URL` | — | PostgreSQL connection string |
+| `CORS_ORIGIN` | `*` | Allowed origin for CORS headers |
+
+## Data Sources
+
+- **Binance** — WebSocket trade stream (`btcusdt@trade`), throttled to 5s writes
+- **Kraken hourly** — OHLC candles polled at HH:01:00 UTC
+- **Kraken daily** — OHLC candles polled at 00:01:00 UTC
+
+## Tech Stack
+
+Clojure · Kit · Undertow · Reitit · PostgreSQL · conman · Migratus