🛡️ Sentinel: [CRITICAL] Fix SQL injection in SQLite PRAGMA

[mapleleaflatte03]

🚨 Severity: CRITICAL
💡 Vulnerability: The MERIDIAN_OBSERVABILITY_SQLITE_JOURNAL_MODE environment variable was directly interpolated into an SQLite PRAGMA statement without proper allowlisting. Since SQLite PRAGMA queries cannot be parameterized, this exposed a SQL injection vulnerability via configuration poisoning.
🎯 Impact: An attacker who can control this environment variable could inject arbitrary SQLite configurations or trigger SQL syntax errors, potentially bypassing intended observability database rules.
🔧 Fix: Implemented strict allowlisting for the journal mode configuration. The value is now checked against a set of explicitly valid modes ('DELETE', 'TRUNCATE', 'PERSIST', 'MEMORY', 'WAL', 'OFF', '', 'DEFAULT'). If an invalid value is supplied, it safely defaults to 'WAL'.
✅ Verification: Ran the intelligence test suite. Verified that the fallback to 'WAL' occurs securely and that valid configurations are correctly processed.

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PR created automatically by Jules for task 4602589750294193991 started by @mapleleaflatte03

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