feat: add Docker image with cron-based scheduled monitoring (Fixes #28)

[lb1192176991-lab]

What

Packages solana-rug as a Docker image with a built-in cron-like scheduler. Background monitoring without requiring an active terminal session.

Why

The CLI watch command requires an active terminal. A Docker container runs in the background on any VPS, NAS, or cloud server — making solana-rug deployable as an infrastructure component.

What's included

Dockerfile

• Based on python:3.12-slim (~120MB base)
• Installs solana-rug from source
• Healthcheck: checks SQLite history file exists
• SIGTERM/SIGINT graceful shutdown via trap

docker-entrypoint.sh

• Reads WATCH_TOKENS (comma-separated mint addresses)
• Configurable WATCH_INTERVAL (default: 300s)
• Optional WEBHOOK_URL for HTTP alerts
• Optional THRESHOLD score threshold
• Persistent SQLite via /data volume mount
• Iterates through watch list and sleeps between iterations

docker-compose.yml

• Ready-to-use Compose file with restart policy and volume mount

Environment Variables

Variable	Default	Description
WATCH_TOKENS	(required)	Comma-separated mint addresses
WATCH_INTERVAL	300	Check interval in seconds
WEBHOOK_URL	""	Optional webhook for alerts
THRESHOLD	""	Score alert threshold
SQLITE_HISTORY	/data/history.sqlite3	Persisted history path

Fixes: #28

[codegraphtheory]

Superseded by #48 (re-applied on latest main).