Adds Prefect 3 documentation (https://docs.prefect.io/v3/) as a built-in source.

[griggz]

✨ What’s inside

• docs.jsonl – one new entry:

  { "name": "Prefect", "crawlerStart": "https://docs.prefect.io/v3/get-started", "crawlerPrefix": "https://docs.prefect.io/v3/" }

• Ran ./scripts/reorder.sh to alphabetize and de-dupe the list; diff is minimal and neatly sorted.

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🤔 Why Prefect?

• Developer Relevance: Widely-adopted Python orchestration framework
• Stable URL structure: All v3 docs live under a single /v3/ prefix, preventing crawler bleed-over into legacy content
• High search value: Frequent target for workflow/ETL questions; having built-in docs removes context-switching for users.

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✅ Pre-merge checklist

• Added a single JSONL object with correct start & prefix URLs
• Executed scripts/reorder.sh successfully (no duplicate keys / format issues)