🛡️ Sentinel: [CRITICAL] Fix SQL injection in StockController

[ManupaKDU]

🚨 Severity: CRITICAL
💡 Vulnerability: SQL/JPQL Injection via string concatenation in StockController search queries.
🎯 Impact: Attackers could inject arbitrary SQL to bypass authentication or extract sensitive database information.
🔧 Fix: Replaced string concatenated queries with secure parameterized queries (:paramName) using a Map.
✅ Verification: Ensure the stock auto-complete searches work normally. Tests were passed (mvn clean test).

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PR created automatically by Jules for task 8210752446963885622 started by @manupawickramasinghe

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