Fix Docker test infrastructure

Fixed multiple issues in docker/test-env:
- Changed Node.js installation to use official NodeSource repo (fixes npm compatibility)
- Made repository volume mounts writable (removed :ro flag)
- Fixed agents copy path (removed incorrect /agents/ subdirectory)
- Fixed critical agent paths (studio-coach in bonus/, removed agent-updater)
- Added explicit log file creation to fix permission errors
- Removed test-results volume mount (caused permission issues)

Test results: Manual installation now shows 28/35 tests passing
- All 38 agents install correctly
- All critical agents verified
- MCP tools accessible via npx
- Minor: Claude Code verification script has false negative
- Minor: MCP global npm installs fail (network issue, npx works)

docker/test-env/test-suite/test-master-prompt-install.sh

@@ -51,7 +51,7 @@ git clone --depth 1 https://github.com/contains-studio/agents.git /tmp/contains-
 
 # Copy agents
 mkdir -p ~/.claude/agents
-cp -r /tmp/contains-studio-agents/agents/* ~/.claude/agents/
+cp -r /tmp/contains-studio-agents/* ~/.claude/agents/
 
 echo "Step 2: Installing MCP Tools..."