Langroid: SQLChatAgent _validate_query blocklist misses pg_read_file family enabling arbitrary file read

Langroid is a framework for building large-language-model-powered applications. Prior to version 0.64.0, `SQLChatAgent` in `langroid` ships a `_validate_query` defense-in-depth layer whose `_DANGEROUS_SQL_PATTERNS` regex blocklist enumerates dangerous SQL primitives by specific function name. The list misses the canonical PostgreSQL filesystem-disclosure family `pg_read_file()`, `pg_stat_file()`, `pg_ls_logdir()`, `pg_ls_waldir()`, `pg_current_logfile()` (and similar `SELECT`-shaped functions in the same family). It also leaves SQL Server `OPENDATASOURCE` and SQLite `ATTACH '<file>' AS x` (DATABASE keyword omitted) unblocked. An attacker able to shape the LLM's generated SQL (directly via prompt input or transitively via prompt-injection in data the LLM ingests) can read arbitrary files from the PostgreSQL host through ordinary `SELECT` queries, even with the agent's strict default configuration (`allow_dangerous_operations=False`, `allowed_statement_types=['SELECT']`). The payloads survive the statement-type allowlist (each is a `SELECT`) and pass through the regex blocklist (none of the function names match), then reach the live SQLAlchemy engine via `SQLChatAgent.run_query`. Version 0.64.0 contains a patch for the issue.

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