[docs/readme] Rewrite README problem framing narrative (why HAMi, architecture positioning)

[mesutoezdil]

Context

This issue is part of the HAMi v2.9.0 Documentation Revamp Plan (WS2 - README Redesign).

PR #201 expanded the README from 40 to 190 lines and consolidated overlapping sections. The remaining work covers all five pending tasks in WS2.

Before you start

Please reach out to the maintainers before picking this up. The positioning narrative must reflect the project's official direction.

• @rootsongjc (author, owns the project narrative)
• @mesutoezdil (revamp reviewer, scope alignment)

Scope

All five tasks below are in scope for this issue. They can be split across multiple PRs if needed - coordinate with the maintainers on sequencing.

1. Rewrite project positioning (problem framing)

Write a "Why HAMi" section that answers:

• What problem exists in running AI workloads on Kubernetes without HAMi
• Where HAMi fits in the Kubernetes and AI infrastructure stack
• Why existing solutions (raw GPU passthrough, static partitioning) are insufficient

Avoid feature listing. Focus on the problem and the gap HAMi fills. Two to four short paragraphs maximum.

2. Architecture overview

Write or substantially expand the architecture section:

• Describe the high-level architecture in plain text (diagram will follow in WS4 via [docs/diagram] Inventory all existing diagrams across the repository #413)
• Separate control plane responsibilities from data plane responsibilities
• Name the key components and their roles without going deep into implementation

3. Replace outdated screenshots

Review all screenshots currently in the README. Replace any that show outdated UI, outdated version numbers, or do not match the current state of the project.

4. Add ecosystem integrations section

Add a section listing the projects and tools HAMi integrates with (vLLM, Volcano, monitoring tools, cloud providers). Each entry should include a one-line description of what the integration enables.

5. Update governance and contribution links

Verify that all links to governance docs, contributing guides, and community channels are correct and point to current pages.

Suggested README structure (for reference)

1. What is HAMi
2. Why HAMi (problem framing) - task 1 above
3. Architecture (high-level) - task 2 above
4. Key capabilities
5. Ecosystem integrations - task 4 above
6. Quick start
7. Community and governance - task 5 above

Acceptance criteria

• "Why HAMi" section present in README.md before the quick start
• Architecture section separates control plane from data plane
• All screenshots are current
• Ecosystem integrations section lists at least vLLM, Volcano, and one monitoring tool
• All governance and contribution links resolve correctly
• No first-person language
• No marketing language ("powerful", "seamless", "cutting-edge")
• No emoji
• DCO sign-off required on every commit (git commit -s)