docs: streamline README and update SESSION_CONTEXT, archive outdated docs

- Streamline README.md from 645 to 365 lines (43% reduction)
- Remove duplicate content with other documentation files
- Focus README on quick start, features overview, and links to detailed docs
- Update SESSION_CONTEXT.md with recent changes (342/342 tests, matching runs audit)
- Archive outdated documentation:
  - CONTEXT.md (duplicated in README)
  - QUICKSTART.md (mentions mock auth, outdated)
  - QUICK_TEST.md (outdated)
- Keep SESSION_CONTEXT.md active for context restoration

docs/archive/QUICK_TEST.md

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+# Quick WebRTC Test Checklist
+
+## Setup (2 browser windows)
+
+**Window 1:** Login as `john@example.com` / `Dance123!`  
+**Window 2:** Login as `sarah@example.com` / `Swing456!`
+
+## Test Steps
+
+### 1. Create Match
+- [ ] User A: Go to event → Request match with User B
+- [ ] User B: Accept match
+- [ ] Both: Navigate to match chat
+
+### 2. Establish WebRTC Connection
+- [ ] User A: Click "Send video (WebRTC)"
+- [ ] User A: Select a small video file (~5-10MB)
+- [ ] User A: Click "Send video (P2P)"
+- [ ] Both: Status shows "Connecting..." → "Connected (P2P)" ✅
+
+### 3. File Transfer
+- [ ] User A: See progress bar 0% → 100%
+- [ ] User B: See "📥 Receiving: [filename]"
+- [ ] User B: File downloads automatically when complete
+- [ ] Both: Chat message appears: "📹 Video sent: [filename]"
+
+## Console Logs to Check (F12)
+
+**User A:**
+```
+📤 Sent WebRTC offer
+📤 Sent ICE candidate
+✅ DataChannel opened
+📤 Sent file metadata
+📤 Sent chunk 1/X
+✅ File transfer complete
+```
+
+**User B:**
+```
+📥 Received WebRTC offer
+✅ DataChannel received
+📥 Receiving file
+📥 Received chunk 1/X
+✅ File received and downloaded
+```
+
+## Success Criteria
+
+✅ Connection state: "Connected (P2P)" with green dot  
+✅ Transfer completes: 100% on both sides  
+✅ File downloads on receiver side  
+✅ File size matches original  
+✅ No errors in console
+
+## If Something Fails
+
+1. Check both users are in same match chat
+2. Check Socket.IO is connected (message input not disabled)
+3. Check browser console for errors
+4. Try refreshing both windows
+5. See docs/WEBRTC_TESTING_GUIDE.md for detailed troubleshooting
+
+## Start Testing
+
+```bash
+docker compose up --build
+# Then open http://localhost:8080 in two browser windows
+```
+
+🚀 **Ready to test!**