docs: add Why HAMi, Architecture, and Ecosystem sections to README

[mesutoezdil]

Adds three sections to README.md per issue #418 (WS2 - README Redesign).

Changes

• Why HAMi: problem framing - what breaks without GPU virtualization, why MIG is insufficient, how HAMi fills the gap
• Architecture: control plane (scheduler extender, mutating webhook) and data plane (device plugin, libvgpu) described separately
• Ecosystem Integrations: table covering vLLM, Volcano, Prometheus, Grafana, NVIDIA GPU Operator

Governance and contribution links verified (HTTP 200).

Build passes for both en and zh locales.

Closes #418

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