feat: deploy wallet app in local k3s

[harshgupta6789]

Summary

• add a wallet_app deployment step to k3s/up.sh
• build, import, deploy, and readiness-check the wallet web image
• expose and health-check the wallet UI at http://localhost:8088/wallet/
• clean up the wallet namespace and image in k3s/down.sh
• document the standalone wallet deployment command
• update the wallet-app submodule to the deployment commit from feat: add local k3s wallet web deployment treetracker-wallet-app#793

Why

The local k3s environment currently deploys the backend and admin client but not the wallet web application requested in #8.

Dependency

This PR depends on Greenstand/treetracker-wallet-app#793.

Validation

• bash -n k3s/up.sh k3s/down.sh
• Kubernetes manifest YAML parsing
• git diff --check
• full Docker/k3s execution was intentionally deferred because the development machine does not currently have sufficient free disk space