CRITICAL: Race Condition in generate_ticket_number()

### Is there an existing issue for this?

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### What happened?

I**ssue Overview**
The generate_ticket_number() trigger on the tickets table can generate duplicate ticket numbers when multiple tickets are inserted concurrently. This is a race condition in the current logic.

**Steps to Reproduce**
Insert multiple tickets at the same time (concurrent inserts).
Observe that two or more tickets may get the same ticket_number.

**Expected Behavior**
Each ticket should receive a unique ticket number, even if multiple inserts happen simultaneously.

**Actual Behavior**
Duplicate ticket numbers are generated.
Inserts may fail due to primary key conflicts.
Numbering is inconsistent under concurrent load.

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