docs: reorganize documentation structure for better context efficiency

Reorganization changes:
1. Moved from root → docs/:
   - QUICKSTART.md
   - QUICK_TEST.md
   - WEBRTC_TESTING_GUIDE.md

2. Created docs/archive/ and moved archival files:
   - COMPLETED.md (completed tasks archive)
   - PHASE_1.5.md (historical phase documentation)
   - RESOURCES.md (learning resources)
   - SECURITY_AUDIT.md (security audit)
   - ADMIN_CLI.md (CLI documentation)

3. Updated all references in:
   - README.md
   - docs/CONTEXT.md
   - docs/TODO.md
   - docs/SESSION_CONTEXT.md
   - docs/DEPLOYMENT.md
   - docs/QUICK_TEST.md

Active docs/ now contains only essential files:
- SESSION_CONTEXT.md (primary for context restoration)
- TODO.md
- CONTEXT.md
- ARCHITECTURE.md
- DEPLOYMENT.md
- MONITORING.md
- QUICKSTART.md
- QUICK_TEST.md
- WEBRTC_TESTING_GUIDE.md

Benefits:
- Reduced token usage when reading docs/ for context
- Clear separation between active and archived documentation
- Better organization for future maintenance

docs/SESSION_CONTEXT.md

@@ -119,8 +119,11 @@
     ├── CONTEXT.md             # Full project description
     ├── TODO.md                # Task list
     ├── ARCHITECTURE.md        # Technical details
-    ├── COMPLETED.md           # Completed tasks archive
-    └── RESOURCES.md           # Learning resources
+    ├── QUICKSTART.md          # Quick start guide
+    ├── WEBRTC_TESTING_GUIDE.md # WebRTC testing
+    └── archive/               # Archived docs
+        ├── COMPLETED.md       # Completed tasks archive
+        └── RESOURCES.md       # Learning resources
 ```
 
 ---
@@ -438,8 +441,8 @@ RUN apk add --no-cache openssl
 - `docs/ARCHITECTURE.md` (technical details)
 
 **Archives:**
-- `docs/COMPLETED.md` (completed tasks)
-- `docs/RESOURCES.md` (learning resources)
+- `docs/archive/COMPLETED.md` (completed tasks archive)
+- `docs/archive/RESOURCES.md` (learning resources)
 
 ---