[Docs] Improve API Documentation with Sequence Diagrams

[Abd-Standard]

Description

Enhance the developer documentation by adding sequence diagrams that illustrate how notifications flow between clients, backend services, smart contracts, and subscribers. This will make the project easier to understand for new contributors.

Tasks
Add Mermaid sequence diagrams.
Document notification request flow.
Illustrate event processing lifecycle.
Link diagrams from README.md and ARCHITECTURE.md.
Verify diagrams render correctly on GitHub.

Acceptance Criteria
Sequence diagrams accurately represent the system.
Documentation is easy to follow.
All diagrams render correctly.
Cross-links between documentation files are valid.

Contributors start work by running:
git checkout -b docs/api-sequence-diagrams

[WorldsBestSoftwareDeveloper]

I'd like to work on this issue.

I've recently completed several GrantFox contributions involving documentation improvements, API refactors, reusable components, and architecture updates across multiple repositories. This issue is a good fit because it combines documentation clarity with understanding how application components interact end to end.

My approach will be to first trace the notification flow through the client, backend services, smart contracts, and subscriber pipeline, then create clear Mermaid sequence diagrams that accurately reflect the implementation. I'll document both the notification request flow and the event processing lifecycle, add cross-links from README.md and ARCHITECTURE.md, and verify that every diagram renders correctly on GitHub. The final documentation will be easy to follow for new contributors while remaining consistent with the existing architecture.

I'll submit a clean, well structured PR that satisfies all acceptance criteria and is straightforward to review.

[AbuJulaybeeb]

Hi Maintainer, haven reviewed the description of the issue, and well experienced with Js Library,
I would like to hop on the issue and sure to deliver at ETA 2hrs

[GBOYEE]

For the API docs sequence diagrams (#354), I'll add Mermaid diagrams to docs/ showing the notification flow: client → backend → smart contract → subscriber. I'll cover:

1. Notification creation flow (sender → contract → event emission)
2. Subscription management flow (subscriber → contract → filter registration)
3. Delivery flow (contract → webhook/websocket → subscriber)

I'll use Mermaid sequenceDiagram blocks in the existing markdown docs. Quick turnaround, ready on assignment.

[YfengJ]

Hi maintainers, I would like to apply for this issue if it is still available.

If assigned, I will keep this documentation-focused: add GitHub-renderable Mermaid sequence diagrams for notification creation, event processing, and subscriber delivery flows; link them from README.md / ARCHITECTURE.md as appropriate; and verify the diagrams render cleanly. I will wait for assignment or explicit confirmation before starting work.