docs: simplify homepage around value, proof, and action

[gthulhu-work]

Summary

Rework the homepage from a documentation-style information dump into a clearer marketing funnel:

1. Value proposition — what Gthulhu does and why a visitor should care.
2. Proof — two large, immediately visible workload outcomes from free5GC and the vLLM benchmark.
3. Problem → mechanism — explain the execution gap in one short narrative and a 3-step Observe / Target / Control flow.
4. Product capabilities — four scannable capability cards instead of a long mixed list.
5. Vision — Claim2Core appears after current proof/capabilities, clearly framed as the next step.
6. Action — end with a single practical CTA: deploy Gthulhu on a real workload.

Why

The previous result-first homepage had the right evidence, but it still read like several documentation sections stacked together: result table, repeated case studies, current capabilities, Claim2Core, architecture, and contributor links all competed for attention.

This PR reduces repetition and makes the first screen answer three questions quickly:

• What is Gthulhu?
• Does it produce meaningful results?
• What should I click next?

Presentation changes

• add a focused hero block;
• turn free5GC and vLLM evidence into two visual proof cards;
• move CNCF / eBPF / LFX badges below the proof rather than above the product message;
• replace duplicated architecture sections with one concise execution flow;
• add a responsive homepage-specific layout in extra.css;
• keep English and Chinese homepages structurally aligned.

Evidence boundaries

• free5GC results remain linked to the published free5GC community case study;
• vLLM remains explicitly labeled as a reproducible community benchmark under upstream blog review, not a generalized performance guarantee;
• Claim2Core remains presented as roadmap / next-step architecture, not already-implemented functionality.

[Copilot]

🟡 Changes recommended

The PR introduces a dark-mode CSS override bug and adds/keeps target="_blank" links without rel="noopener noreferrer", which should be addressed before approval.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Reworks the English and Chinese homepages from a documentation-heavy landing page into a marketing-oriented funnel (value → proof → mechanism → capabilities → roadmap → CTA) and adds homepage-specific CSS to support the new layout.

Changes:

• Redesign docs/index.md and docs/index.zh.md into structured hero/proof/flow/cards/CTA sections.
• Add a responsive “homepage marketing layout” stylesheet section in docs/stylesheets/extra.css.
• Reorder and restyle the trust/badge row and proof presentation.

File summaries

File	Description
docs/stylesheets/extra.css	Adds homepage-specific hero/proof/flow/CTA layout styles and responsive rules.
docs/index.md	Replaces the homepage with a value/proof/mechanism/capabilities/roadmap/CTA structure (English).
docs/index.zh.md	Mirrors the new homepage structure for the Chinese version to stay aligned.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 3
• Review effort level: Lite

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