docs: add hydra escrow app tutorial with demo video

docs/docs/tutorials/hydra-escrow-app.md

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+# Hydra Escrow App — Tutorial
+
+A 3-party Layer 2 escrow application built on Cardano using Hydra Head Protocol. This tutorial demonstrates a complete escrow workflow using Kuber Hydra's devnet for local development and testing.
+
+## Demo Video
+[Watch Demo](https://drive.google.com/file/d/1Umr9kbSVCq8T7yvPWc9kygNKVT8VQrGm/preview)
+
+## Source Code
+[GitHub — hydra-settlement](https://github.com/prabinpkrl/hydra-settlement)
+
+## Prerequisites
+
+This application requires:
+- **Kuber Hydra devnet** running locally (3 Hydra nodes + cardano-node)
+- See [Local Devnet Setup](https://dquadrant.github.io/kuber/hydra_docusaurus/docs/hydra-js-client/local-devnet) for devnet configuration
+- Node.js 18+ and npm/pnpm
+
+## What it demonstrates
+- Opening a Hydra Head (3 parties commit ADA to L2)
+- Instant zero-fee transactions on Layer 2
+- Escrow flow: lock → release → dispute → mediator resolves
+- Close head + fanout → funds settle back to Cardano L1
+
+## Flow
+1. Buyer creates payment room — all parties commit ADA to L2
+2. Buyer sends protected payment — instant, 0 fees on L2
+3. Seller confirms delivery
+4. Buyer releases or raises dispute
+5. Mediator resolves if disputed
+6. Close + fanout — settled on Cardano L1