[Docs] Rewrite InferenceServer docs for typed Ray Serve and Dynamo backends

[lbliii]

Context

Child of #2118. The Inference Server was restructured after the v1.2.0 code freeze in #1813, #1820, #1833, #1834, and #1861, with platform/runtime follow-ups in #1895, #1957, and #2053.

The current Fern page still imports the removed InferenceModelConfig and presents Ray Serve as the only backend. Its copy-paste examples fail against current main.

Required coverage

• Replace InferenceModelConfig with RayServeModelConfig and RayServeServerConfig.
• Document DynamoVLLMModelConfig, DynamoServerConfig, DynamoRoleConfig, and DynamoRouterConfig.
• Provide runnable Ray Serve, Dynamo aggregated, and Dynamo disaggregated examples.
• Explain model/server config type validation, multi-model rules, replica and tensor-parallel placement, and single-node constraints for disaggregated roles.
• Document router modes, KV event behavior, per-role engine overrides, runtime environment merging, subprocess environment propagation, lifecycle, health checks, and cleanup.
• Explain HAProxy ingress behavior and the final tested dependency stack, including architecture restrictions.
• Include a before/after migration from InferenceModelConfig.
• Incorporate the multimodal, hybrid-KV, subprocess-environment, and false-CLI-flag corrections from #2053.

Target pages

• fern/versions/main/pages/curate-text/synthetic/inference-server.mdx
• Related LLM-client, NDD, installation, and infrastructure pages where they repeat the obsolete API

Acceptance criteria

• No published example imports or references InferenceModelConfig
• Ray Serve quickstart runs with the typed config API
• Dynamo aggregated and disaggregated examples match current constructors and validation rules
• Routing, placement, runtime-env, lifecycle, and cleanup behavior are documented
• CUDA/Ray/PyTorch/vLLM/ai-dynamo requirements and x86_64 restrictions are explicit
• Migration guidance explains the breaking typed-config change
• Related Fern pages are audited for stale examples
• Fern validation and link checks pass

Related PRs: #1813, #1820, #1833, #1834, #1861, #1895, #1957, #2053