docs: add userflow and testing guide

[rahuliitk]

Summary

• userflow.md: Comprehensive user flow documentation covering all 43+ product features, role-based permissions (Admin, Homeowner, Designer, Architect, Contractor, Factory), full project lifecycle from onboarding to post-occupancy maintenance, and end-to-end master flow with visual diagrams
• testingguide.md: 150+ prioritized test cases (P0/P1/P2) organized across 42 modules, complete with environment setup instructions, bug report template, security testing (XSS, SQL injection, auth bypass), performance testing, mobile responsiveness testing, glossary, and a prioritized completion checklist — designed for QA interns to test the entire product independently

Test plan

• Verify both files render correctly on GitHub (markdown formatting, tables, code blocks)
• Review userflow.md for accuracy against current feature set
• Review testingguide.md test cases cover all critical paths
• Confirm no sensitive data (API keys, credentials) in documentation

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