fix: retry ministry scrape on transient network failure

[DerekRoberts]

The scheduled ministry validation job intermittently fails due to unhandled socket hang ups (ECONNRESET) when scraping www2.gov.bc.ca.

• Adds retry logic (3 attempts with exponential backoff) and a 30s timeout to getMinistriesHtml in schema/script/index.js
• Sets a descriptive User-Agent header for scraping www2.gov.bc.ca
• Reads schema/bcgovpubcode.json directly from the local workspace instead of making an unneeded remote fetch to raw.githubusercontent.com
• Adds unit tests covering schema loading, successful HTML fetching, retry on transient failure, and exhaustion of retries

Closes #676

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