docs: update documentation after Phase 1 completion
Updated documentation to reflect completion of Phase 1 (Backend Foundation):
- SESSION_CONTEXT.md: Updated status to Phase 1 completed, ~50% progress
- Added completed backend infrastructure details
- Updated tech stack with actual versions
- Added Phase 2 next steps (Matches API, Ratings, WebRTC)
- Updated key files list with backend files
- Added Prisma OpenSSL bug fix to known issues
- TODO.md: Marked Phase 1 as completed, Phase 2 as active
- Moved Phase 1 steps to completed section with checkmarks
- Added detailed Phase 2 tasks (4 steps: Matches API, Ratings API, WebRTC Signaling, WebRTC File Transfer)
- Reorganized future phases (removed Phase 2 from future, renumbered)
- COMPLETED.md: Added comprehensive Phase 1 completion record
- All 4 steps documented with checkmarks
- Test coverage statistics (81.19% overall)
- Infrastructure updates
- Bug fixes (OpenSSL for Prisma)
- Git commit history for Phase 1
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