Overhaul the "Deployment" section for clarity

[desimone]

Overhaul the "Deployment" section for clarity
Follow-up to #1726

What's incorrect or missing?

• GCP, Kubernetes, Ingress usage scattered across multiple pages
• Hard for users to pick the right approach

What's the resolution?

• Group each deployment target (for example, GCP, K8s, manual) under a coherent structure
• Update cross-links to advanced config (domain registration, TLS, etc.)