docs: polish README links and demo presentation

[SakuraMathcraft]

Summary

Apply the same presentation and link changes to both READMEs:

• Remove the LINUX DO introduction/link.
• Link the user manual to the repository Markdown document using a relative path, instead of downloading a release PDF.
• Link client examples to the relative examples/automation/ directory.
• Display all three recognition demos directly, removing the remaining details/summary wrappers.
• Center the donation/community QR-code table headers and images within their columns.

Validation

• All local Markdown/image destinations exist.
• Both READMEs contain all three demos, three Markdown manual links, and the relative examples-directory link.
• No remaining collapsible sections, LINUX DO references, or Chinese PDF labels.
• git diff --check passed.
• Documentation only: no GIF or application-code changes; no runtime tests/build needed.