Build invoice payment flow visualizer

[Kingsman-99]

Label: complexity: high
Points: 200

Description

Complex invoices with multiple recipients and partial payments are hard to understand without a visual representation. This issue adds generateFlowDiagram(invoiceId) that returns a Mermaid diagram string representing the payment flow.

Technical Context

Involves a new src/flowVisualizer.ts. Fetch invoice and payments. Build a Mermaid flowchart LR diagram with nodes for creator, invoice, and each recipient. Edges show payment amounts. Completed flows shown in green, pending in yellow. generateFlowDiagram(invoiceId): Promise<string> returns the Mermaid string.

Acceptance Criteria

• generateFlowDiagram(invoiceId: string): Promise<string> exported
• Returns valid Mermaid flowchart LR syntax
• Each recipient shown as a separate node
• Payment amounts shown on edges
• Test verifies output contains expected node and edge definitions
• All existing tests pass
• TypeScript strict mode — zero any types

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[Eromosele0110]

@Eromosele0110 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I will like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Eromosele0110 to this issue.

[drips-wave]

Congratulations, @Eromosele0110! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @Eromosele0110: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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