docs: clarify SQL injection plugin responsibilities

[deepsikha-dash]

Description

Clarifies the responsibilities and intended usage of SQL injection related plugins to reduce overlap and improve contributor guidance.

Changes Made
Clarified sqli_checker as a feasibility validation tool focused on identifying potential SQL injection indicators.
Clarified sqlmap as a testing and controlled database enumeration tool.
Clarified sqli_exploiter as an exploitation-focused workflow intended for confirmed SQL injection findings.
Updated plugin metadata, catalog descriptions, and frontend tool descriptions for consistency.
Added guidance describing when each SQL injection plugin should be used.

Related Issues

Closes #546

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

Documentation and metadata changes only. Reviewed updated descriptions in:

• PLUGINS.md
• plugins/sqli_checker/metadata.json
• plugins/sqlmap/metadata.json
• plugins/sqli_exploiter/metadata.json
• frontend/src/data/scanTools.ts

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.

[utksh1]

Applied maintainer cleanup for the blocking items: moved the SQL injection guidance outside the plugin table and refreshed the modified plugin checksums. The PR is now focused docs/metadata copy cleanup; approved pending fresh green checks.