FEAT: VISUAL FILTER BUILDER UI

[somethingwithproof]

SUMMARY
The Syslog plugin currently relies on raw text inputs for 'sql' type rules and simple dropdowns for others. There is no visual interface to build complex, multi-condition logic without manual SQL knowledge.

WHY REFACTOR
Replacing raw SQL inputs with a visual builder improves user experience and is a prerequisite for the backend transition to JSON-based rules (Issue #284). It ensures that users can only construct valid, safe queries through a controlled interface.

PROPOSED CHANGE
Implement a client-side visual Filter Builder:

1. Add a JavaScript component (js/filter-builder.js) that allows users to add/remove rule rows.
2. Provide dropdowns for allowed fields (Host, Facility, Message, etc.) and operators.
3. Serialize the visual state into a JSON string for storage in the existing message column.
4. Integrate the component into the Alert and Removal Rule edit pages.

SCOPE

• Client-side UI implementation in js/filter-builder.js.
• Integration into syslog_alerts.php and syslog_removal.php.
• Ensuring the UI handles both new JSON-based rules and displays a warning for legacy raw SQL rules.