docs(mkdocs): clean content and add short demo

[benbenbang]

This pull request updates the documentation for Tombo to improve clarity and consistency in the feature descriptions. The main changes are the removal of emoji icons from feature headings and lists, and the addition of a more detailed demo section on the index page. These updates make the documentation more professional and easier to read.

Documentation consistency and clarity:

• Removed emoji icons from feature section headings and bullet points in docs/docs/features/overview.md to standardize formatting and improve readability. [1] [2] [3] [4] [5] [6] [7] [8] [9]
• Updated feature list formatting on the index page in docs/docs/index.md by removing emojis and simplifying headings for a more professional presentation.

Demo and onboarding improvements:

• Replaced the step-by-step demo instructions with a video walkthrough and a clearer summary of the workflow in docs/docs/index.md, making it easier for users to understand Tombo’s capabilities.
• Added a small formatting improvement for layout consistency in docs/docs/index.md.

[ptah-technical-app]

🎉 This PR is included in version 1.0.0 🎉

The release is available on GitHub release

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