docs: Visual redesign of README & SVG additions

[Tyleraltight]

Documentation / Visual Redesign

Submission type

• Documentation / Infrastructure Improvement

What changed

This PR completely overhauls the visual layer of the \dify-plugins\ repository. Because the root directory must host hundreds of organization folders (for the marketplace plugin indexer), the repository can appear very dense and intimidating to newcomers.

To solve this, we've implemented a high-quality visual redesign using scalable SVG assets to structure the information architecture, drawing focus away from the dense folder tree and towards a clean, professional ecosystem showcase.

Key Highlights:

• SVG Hero Banner: Added \�ssets/readme/hero.svg\ representing the 400+ plugins connecting into a central hub.
• SVG Workflow Diagram: Added \�ssets/readme/workflow.svg\ mapping out the 4-step publication lifecycle (Develop -> Package -> PR -> Marketplace).
• README Streamlining: Organized badges under the banner, condensed plugin categories into a clear comparison table, and added a clarifying note on why organization folders reside at root.

Risk level

• Low risk
• Medium risk
• High risk

Required checks

• All user-facing text is in English and follows repository formatting standards.
• Added SVG assets are self-contained and GitHub-safe.

[crazywoola]

🤖 CI Summary

Check	Status
Pre Check Plugin	❌ failed — run log
PR Risk Label	✅ pass

What's wrong

The Get PR Path step fails with:

ERROR: Only one .difypkg file change is allowed in a single PR.

This check is designed for plugin package submissions and requires the PR to change exactly one .difypkg file. Your PR only touches README.md and two SVG assets, so it contains zero .difypkg changes and cannot pass this check.

What to do

Nothing is wrong with your changes — this failure is expected for docs-only PRs and does not need to be fixed. Maintainers will review documentation PRs separately from the plugin pre-check.

Thanks for the README improvements! 🙏