docs: Hydrating donate docs in underpopulated sections
Major documentation updates made to:
- Design and architecture
- Written description regarding how and why donate-neo design diverged between initial planning and execution
- Mermaid diagrams outlining both DI-driven data relationships between Django apps and user donation checkout flow
- Technical debt, outlining the friction between donate-neo's PII minimal handling and Stripe Radar's fraud detection algorithm
Minor documentation updates made to:
- Queues, regarding the custom Resque handler and PayPal IPN handling
- Interfaces, regarding PayPal IPN handling
- Implementation, clarifying that CSS and JS are managed via NPM rather than NVM (which itself simply manages local NPM versioning)
- Tests, listing the command for running unit tests