Update test docs

[Martokim]

Summary

This PR includes final documentation updates for the tests/ folder, aligning with the Week 3 deliverables of the CleanCity QA project.

Changes Made

• tests/test-plan.md: Finalized sections on Test Scope, Schedule, Entry/Exit Criteria, and Automation Plan.
• tests/environment.md: Detailed hardware/software tools, browser & device configurations, network setup, and validation steps.
• Confirmed references to defects (DEF-001–DEF-004) and traceability with test cases and functional requirements.
• Tools like axe, WAVE, NVDA, Jest, Lighthouse fully documented.
• Updated responsibilities and environment validation for the team.

Impact

• Supports 100% test case execution for FR-001–FR-097.
• Enables effective manual + automated testing across devices and browsers.
• Provides traceability for deliverables like final-report.md and traceability-matrix.md.

Notes

• All changes are limited to the tests/ folder.
• No code or logic files were modified.
• Ready for review and merge to main once team approves.

cc: @samuel-kimwele-mbai @Bbrnn