feat: add API key authentication and HTTPS support

[viamus]

Description

Add optional API key authentication to protect MCP server endpoints and update all documentation to use HTTPS by default for secure communication.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

Related Issues

N/A

Changes Made

• Add ServerSecurityOptions configuration class for API key settings
• Add ApiKeyAuthenticationMiddleware to validate API key on incoming requests
• Add -ApiKey and -RequireApiKey parameters to PowerShell install script
• Update docker-compose.yml with security environment variables (MCP_API_KEY, MCP_REQUIRE_API_KEY)
• Update .env.example with security configuration documentation
• Add HTTPS launch profile in launchSettings.json
• Update README.md to use HTTPS URLs (https://localhost:5001) for .NET CLI
• Update README.md with complete security documentation section
• Update Claude Code MCP configuration examples to use --header flag for API key

Testing

• I have tested these changes locally
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have updated the documentation accordingly

Screenshots (if applicable)

N/A

Additional Notes

• API key authentication is optional and disabled by default (RequireApiKey: false)
• When enabled, the /health endpoint remains accessible without authentication
• The API key is passed via the X-API-Key header
• For Docker deployments, a reverse proxy (nginx, traefik) is recommended for HTTPS termination
• The install script automatically enables RequireApiKey when an ApiKey is provided