feat: document summarization recipe redesign for journalism use

[aaronbrezel]

Summary

• Adds two optional journalist inputs to the document-summarization recipe: Document Type and Area of Interest
• Rewrites system prompt to a journalist-oriented BLUF structure; optional inputs are conditionally injected via {{#key}}...{{/key}} template blocks
• Extends interpolateTemplate with conditional block syntax (content included only when key is non-empty) — infrastructure the recipe depends on
• Adds integration tests that exercise the recipe template string through interpolation, catching future typos in block syntax

Test Plan

• All 439 tests pass (npm test)
• Typecheck clean (npm run typecheck)
• Build clean (npm run build)
• 12 unit tests cover interpolateTemplate conditional block behavior
• 6 integration tests exercise the recipe template with all input combinations (no inputs / docType only / focus only / both)

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