Create PDP Explorer Backend Architecture Document

[rjan90]

Done Criteria

Create and check in an architecture document for the PDP Explorer backend system to the GitHub repository. The document should clearly explain the system's design, recent database changes, and integration points to enable easy onboarding and maintenance.

• Architecture document created and checked into GH repo
• Includes database schema and indexer integration
• Covers API design and data flow
• Reflects current integration status with frontend

Why Important

A well-documented architecture document ensures maintainability, facilitates knowledge transfer, and supports future development of the PDP Explorer.

User/Customer:

• Development team, operations team, and future maintainers

[rjan90]

Branch for documentation is here: https://github.com/FilOzone/pdp-explorer/tree/docs/indexer. It will be merged once completed.

[ZenGround0]

Also generated this which is good for a high level: https://www.notion.so/filecoindev/PDP-Explorer-Architecture-1b1dc41950c180ed8c67fb6e9d4c8844

[BigLep]

Branch for documentation is here: https://github.com/FilOzone/pdp-explorer/tree/docs/indexer. It will be merged once completed.

I think it could be useful to open this as a PR so it's easier for folks to comment inline or add questions.

https://www.notion.so/filecoindev/PDP-Operational-Readiness-Review-1b3dc41950c180159714f4eb77d438c3?pvs=4 has some questions that would likely be good to include in that doc (although certainly not all of that doc is relevant. I could help extract relevant questions if useful.)

[rjan90]

Docs PR has been opened here: #32