Missing plugin samples ("hello-world" and others) and outdated references

[aroslanov]

Documentation and third-party resources (e.g., @toeverything/awesome-affine) reference several plugin sample directories such as https://github.com/toeverything/AFFiNE/tree/master/plugins/hello-world, but these now return 404 errors. Additionally, other referenced plugin samples in the /plugins directory are also missing from the repository.

Steps to Reproduce:

1. Visit referenced URLs such as:

• https://github.com/toeverything/AFFiNE/tree/master/plugins/hello-world
• https://github.com/toeverything/AFFiNE/tree/master/plugins/ (and any other plugin samples)

2. Observe the 404 errors.

3. Search the repository for plugin samples or templates, but none are found.

Expected Behavior:

• Official plugin samples (e.g., "hello-world" and others) should be available in the repository.
• Documentation and awesome lists should reference valid, up-to-date sample locations.

Actual Behavior:

• Referenced links are broken.
• No minimal plugin template or sample is available for new developers.

Additional Context:

• This makes it difficult for new contributors to get started with plugin development for AFFiNE.
• A set of minimal, well-documented plugin samples would greatly help onboarding and community growth.

Request:

• Please restore or provide official minimal plugin samples in the repository (including "hello-world" and others).
• Update documentation and third-party references accordingly.