Extract AppDynamics-specific logic from Monkey.js into a plugin system

[svrnm]

Summary

The core replacement engine (Monkey.js) contains hardcoded AppDynamics-specific corner cases. These should be isolated behind a plugin or namespace hook so vendor-specific behavior is extensible without modifying the core engine.

Problem

AppDynamics-specific logic (special DOM handling, namespace commands in src/commands/appdynamics/) is woven into the core engine. This makes the engine harder to understand and couples it to one vendor's UI patterns.

Suggested approach

• Define a plugin interface that namespaced command sets can implement (e.g., beforeApply, afterApply, custom DOM walkers)
• Move AppDynamics-specific branches in Monkey.js behind this interface
• Register the appdynamics namespace as the first plugin
• Ensure existing @namespace[] = appdynamics configs continue to work unchanged

Risks

• Must preserve backward compatibility with existing configurations
• Performance impact of plugin dispatch in the hot loop needs measurement