Create: `insights/developer-lifecycle` Notebook

[ccerv1]

Current State: Partially built - has basic lifecycle visualization built on top of outdated model.

Vision: Enhanced with metrics and comparison features

Current Features:

• Shows monthly trends of new, churned, and active contributors
• Ecosystem selector
• Activity/inactivity toggle
• State transition visualizations

Enhancements Needed:

1. High-Level Lifecycle Metrics Panel:
   • Ratio of churn over past year
   • Ratio of churn over all time
   • Number of dormant developers currently
   • Number of dormant developers over last 6 months
   • (Need to be thoughtful about best metrics - may need refinement)
2. Comparison Feature:
   • Apples-to-apples comparison of ecosystems (e.g., Ethereum vs. Solana)
   • Show overlaps among developers
   • Side-by-side lifecycle comparisons
3. Period Flexibility:
   • Currently uses monthly periods (OSO definition)
   • Goal: Also support 28-day periods (Electric Capital definition)
   • Allow toggling between definitions
4. Additional Context:
   • Better explanation of what each lifecycle stage means
   • Show transition paths more clearly

[linear]

OSO-1431