refactor: consolidate LocalMetrics into one native host

[louresb]

What changed

• Consolidates native collection, API, Prometheus output, and Blazor into one ASP.NET Core process.
• Separates platform collectors and cache logic into LocalMetrics.Core.
• Fixes live chart updates and responsive dashboard rendering.
• Keeps NGINX as an optional proxy to the native host and updates the project documentation.

Validation

• Release build: 0 warnings, 0 errors
• Tests: 8 passed on Windows
• Dashboard validated at desktop and mobile widths
• JSON and Prometheus endpoints verified
• Docker Compose configuration validated