Restructure presentation as story-driven narrative

[mryhmln]

Summary

• Rewrites the Blueprint Overview presentation from a 22-slide feature catalog into a 14-slide story-driven narrative following a state's modernization journey
• Introduces Blueprint (contracts) and Safety Harness (delivery accelerators) as the two core concepts
• Uses real examples from the harness branch (federal CSV data model, California overlay) with side-by-side analyst/developer views
• Renames presentation files from safety-net-openapi-overview to safety-net-blueprint-overview

Key changes

• Narrative flow: CfA Blueprint intro → problem (lock-in + slow to build) → vision → solution → 6 stages → payoff
• Persona-driven stages: each stage shows who does what (program analyst, developer, designer)
• Accessible language: replaced jargon (adapter→connector, mock server→simulated server, annotations→field-level context, etc.)
• Blueprint/Harness framing: Blueprint = portable contracts you own; Safety Harness = delivery accelerators (form previews, simulated servers, code libraries, automated checks)
• Real examples: federal data model CSV, California state overlay (SNAP→CalFresh rename, language additions), form definitions
• File rename: safety-net-openapi-overview → safety-net-blueprint-overview with all references updated

Test plan

• Run npm run docs:slides to verify Marp build succeeds
• Open generated HTML and review all 14 slides for content, layout, and readability
• Verify no slides overflow their content area
• Check links in README, index.html, and executive-summary still work