[codex] Mask SQL literals in query_graph guard

[yibeichan]

Summary

• port SQL literal/comment masking to the TypeScript query_graph guard
• allow valid SELECT usage of SQLite REPLACE()
• keep write-keyword rejection for executable SQL text outside literals/comments
• add regression coverage for REPLACE(), string literals, and comments

Root cause

queryGraph scanned the raw SQL text for write keywords before execution. That rejected safe SELECT queries when a blocked word appeared as a SQLite function name, in a string literal, or in a comment. The Python CLI already masks literals/comments before keyword checks; the MCP path did not.

Validation

• npm test -- --testPathPatterns=query-graph-tool.test.ts
• npm test

Closes #200