docs: refresh general graph documentation

[SamuelSupe]

What changed

• Refresh the English and Chinese README files to describe GraphDB as a general-purpose entity-relationship graph database.
• Clarify that CMDB, topology, dependency, lineage, and asset relationships are supported scenarios.
• Align architecture, database introduction, query examples, capability gaps, and bilingual user guides with the current domain-neutral core.
• Mark CI types, identity reconciliation, source governance, and collector-specific guidance as optional or scenario-specific where appropriate.

Why

The documentation previously presented GraphDB as an internal CMDB-only database, which no longer matches the current product positioning and API model.

Validation

• git diff --check passed.
• Only the 18 intended documentation files are included; unrelated internal/.DS_Store remains untracked and was not included.