docs: add diagrams-as-code for payment flows and escrow lifecycle

[gospeltout]

Summary

Added comprehensive diagrams-as-code and technical documentation for payment flows, escrow lifecycle state transitions, dispute resolution, and economic reconciliation. Also integrated illustrated empty states with guidance CTAs across all list views.

Changes

• Payment & Escrow Lifecycle Docs: Created docs/architecture/payment-escrow-lifecycle.md featuring an Escrow State Machine matrix and 6 Mermaid sequence diagrams (Task Funding & Bidding, Token Locking, Escrow Release, Escrow Refund, Dispute Resolution, and Ledger Reconciliation) matching Soroban smart contracts (agent_bidding, dispute_resolution).
• Architecture Overview: Updated docs/architecture/index.md with an embedded Payment & Escrow Architecture section.
• Node Operators Guide: Added Step 6.4 to docs/NODE_OPERATORS_GUIDE.md detailing settlement guidelines and juror dispute participation.
• Glossary: Updated docs/GLOSSARY.md with escrow lifecycle sequence diagram cross-references.
• Illustrated Empty States: Created reusable EmptyState component (EmptyState.tsx, EmptyState.module.css, EmptyState.test.tsx) and applied it to Tasks, Agents, History, Payments, and Notifications list pages.

Verification & Testing

• npm test (Backend/Frontend) — 34/34 test files & 251/251 tests passing.
• cargo fmt --check (Smart Contract formatting)
• Mermaid diagram syntax & rendering validation across markdown docs.

Contributor Checklist

• PR title follows Conventional Commits (docs(architecture): add diagrams-as-code for payment flows and escrow lifecycle (#354))
• All CI checks pass locally
• Documentation updated in docs/ or README.md if applicable
• No secrets or credentials committed

Closes #374

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