🔒 Fix: Missing Input Validation for Transaction Quantity

[alfieprojectsdev]

This PR addresses a security vulnerability where the transaction form allowed invalid quantities (e.g., 0 or negative numbers for dispensing) to be submitted.

Changes:

• Implemented strict validation checks in handleDispense, handleReceive, and handleAdjust.
• Added an error message display in the UI.
• Ensured ADJUST still supports negative numbers for stock corrections, while preventing 0.
• Ensured DISPENSE and RECEIVE only accept positive quantities to avoid confusion and potential double-negative logic issues.

Verification:

• Verified manually using a Playwright script that 0 and negative inputs are blocked for Dispense/Receive, but allowed for Adjust (negative).
• Verified that valid inputs still work.
• Ran linting and build checks.

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PR created automatically by Jules for task 9937947492711592989 started by @alfieprojectsdev

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