Adapter architecture for pluggable country-specific scrapers

[Metrohan]

Summary

Design a pluggable adapter system so any contributor can add a country-specific scraper without modifying core scraper infrastructure.

Why

Currently each scraper is hardcoded into SCRAPER_FUNCS. As we scale to dozens of countries, we need auto-discovery and a standard adapter interface.

Acceptance criteria

• Scraper adapter interface defined (e.g. BaseEventScraper ABC)
• Auto-discovery: any class in app/scrapers/ implementing the interface is registered automatically
• Each adapter declares its source_name, country, and scrape() method
• Existing scrapers migrated to the new interface
• Contributor docs updated in CONTRIBUTING.md

Phase

Roadmap Phase 4 — Internationalization