docs: expand generic graph GQL examples

[SamuelSupe]

What changed

• Expand the English and Chinese READMEs with generic graph GQL examples.
• Update the quick-start GQL query to show projection and clarify application-defined entity kinds, properties, and relationship types.
• Link readers to the GQL guide for traversal, pagination, EXPLAIN, and PROFILE.

Why

Make the general-purpose graph positioning concrete beyond CMDB examples.

Validation

• git diff --check passed.
• git diff --cached --check passed.
• Only README.md and README.zh-CN.md are included; unrelated internal/.DS_Store remains untracked.