[codex] Improve README focus and preview

[hetaoBackend]

Summary

• Rewrite the English README around the core AgentForge value proposition, quick start, capabilities, architecture, API example, channels, and development flow.
• Mirror the same clearer structure in README.zh.md so the Chinese README no longer keeps the old setup flow.
• Replace the old dark UI screenshot with a clean light macOS-style SVG preview and remove the stale PNG asset.

Validation

• Checked that README files no longer reference assets/screenshot.png or old setup commands like make install-deps / make package-dmg.
• Ran git diff --check origin/main...HEAD.
• Rendered the SVG preview locally through Quick Look for a visual sanity check.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
agentforge-landing	Ready	Preview, Comment	Jun 13, 2026 3:15am