Add Memind UI admin console

[starboyate]

Summary

• Add a standalone Vite/React Memind UI admin console for local memory inspection and maintenance.
• Implement typed admin API clients, memory scope handling, dashboard, buffers, raw data, memory items, item graph, memory threads, settings, and retrieve/debug views.
• Add frontend mock API mode for UI review with rich deterministic data, plus open CORS support for local server integration.

Test Plan

• pnpm build in memind-ui
• pnpm lint in memind-ui
• pnpm test in memind-ui
• mvn -pl memind-server test

Security Notes

• The UI is documented as local-only and unauthenticated.
• The PR diff was checked for common secret patterns before creation.
• memind-server/src/main/resources/application.yml is not included in this PR diff.