docs: add missing ivorysql prefix to Oracle GUCs

[Yanghanrui666]

Closes #267

Summary

• Add the full ivorysql. prefix to user-facing Oracle GUC references.
• Cover identifier_case_switch, datetime_ignore_nls_mask, and compatible_mode in English and Chinese documentation.
• Keep internal C variable names unchanged where the design documents intentionally show source code.

Validation

• git diff --check passes.
• Searched the updated master documentation for the affected GUC names.
• Confirmed the only remaining unprefixed occurrences are internal source-code variables, not user-facing parameter names.

[github-actions]

🚀 IvorySQL-Docs Preview Ready

• Chinese Preview: https://pr-318-doc--delicate-lolly-113d3b.netlify.app
• English Preview: https://pr-318-doc--delicate-lolly-113d3b.netlify.app/en