Task 373: External Link Validation for Reports

Status: DONE

Motivation

CLAUDE.md requires: "External source links: All external source citations (NASA NTRS, papers, worldbuilding documents) must be rendered as clickable hyperlinks, not plain text."

Currently, internal links between reports are validated (report-data-validation.test.ts), but there is no validation of external URLs. With ~72 external URLs across episode and summary reports, link rot or formatting issues could degrade reader experience.

Scope

1. Add tests that extract all external URLs from episode and summary reports
2. Validate URL format (proper https://, no truncation, no malformed encoding)
3. Check for common issues: duplicate URLs, plain-text URLs not wrapped in links, HTTP vs HTTPS
4. Ensure external source citations in reports are actually rendered as clickable <a> tags (not just plain text URLs)
5. Validate known domains are reachable patterns (not runtime HTTP checks, but structural validation)

Non-goals

• Runtime HTTP link checking (requires network access, flaky in CI)
• Fixing any content issues in reports (separate tasks if found)