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-manual-install.sh

@@ -53,7 +53,7 @@ fi
 # Copy agents
 log_info "Copying agents to ~/.claude/agents..."
 mkdir -p ~/.claude/agents
-if cp -r /tmp/contains-studio-agents/agents/* ~/.claude/agents/ >> "$LOG_FILE" 2>&1; then
+if cp -r /tmp/contains-studio-agents/* ~/.claude/agents/ >> "$LOG_FILE" 2>&1; then
     test_pass "Agents copied successfully"
 else
     test_fail "Failed to copy agents"