Update documentation with last updated dates and improve navigation indexes

- Added "Last Updated" date to multiple documentation files for better tracking.
- Enhanced the README with quick navigation indexes for guides, references, and architecture documentation.
- Updated titles in Keycloak deployment and testing guide for consistency.

docs/REFERENCE_INDEX.md

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+# Reference Documentation Index
+
+**Last Updated**: 2025-01-09
+
+This index provides quick access to all reference documentation, API documentation, and technical specifications.
+
+## API Documentation
+
+- **[API Documentation](./API_DOCUMENTATION.md)** - Complete API reference
+- **[API Contracts](./api/API_CONTRACTS.md)** - API contract specifications
+- **[API Examples](./api/examples.md)** - API usage examples
+
+## Proxmox Reference
+
+- **[Proxmox Reference Documentation](./proxmox/reference/)** - Proxmox reference docs
+  - [API Tokens](./proxmox/reference/API_TOKENS.md) - API token management
+  - [Site Mapping](./proxmox/reference/SITE_MAPPING.md) - Site configuration
+  - [Resource Inventory](./proxmox/reference/RESOURCE_INVENTORY.md) - Available resources
+  - [Image Inventory](./proxmox/reference/IMAGE_INVENTORY.md) - VM images
+  - [Image Requirements](./proxmox/reference/IMAGE_REQUIREMENTS.md) - Image specifications
+  - [Instance Inventory](./proxmox/reference/INSTANCE_INVENTORY.md) - Instance tracking
+
+## Specifications
+
+- **[VM Specifications](./VM_SPECIFICATIONS.md)** - Complete VM specifications
+- **[Hardware BOM](./hardware_bom.md)** - Hardware bill of materials
+- **[VM Deployment Checklist](./VM_DEPLOYMENT_CHECKLIST.md)** - Deployment checklist
+
+## Data Models
+
+- **[Data Model](./architecture/data-model.md)** - GraphQL schema and data model
+- **[Tech Stack](./architecture/tech-stack.md)** - Technology stack details
+
+## Configuration References
+
+- **[Environment Variables](../ENV_EXAMPLES.md)** - Environment variable reference
+- **[Proxmox Environment Variables](./proxmox/ENVIRONMENT_VARIABLES.md)** - Proxmox configuration
+- **[Proxmox Credentials](./proxmox/PROXMOX_CREDENTIALS.md)** - Credentials management
+
+## Script References
+
+- **[Script Reference](./proxmox/SCRIPT_REFERENCE.md)** - Utility scripts documentation
+- **[Scripts README](../scripts/README.md)** - Scripts directory overview
+
+---
+
+**See Also:**
+- [Guides Index](./GUIDES_INDEX.md) - All how-to guides
+- [Architecture Documentation Index](./ARCHITECTURE_INDEX.md) - Architecture documentation
+- [Main Documentation Index](./README.md) - Complete documentation index
+