feat(environment): introduce disable_omo_env configuration option

- Added a new configuration option `disable_omo_env` to control the injection of the `<omo-env>` block in agent prompts.
- Updated relevant functions and tests to support this feature, ensuring that the environment context can be toggled on or off as needed.
- Enhanced documentation to reflect the new option and its implications for API cost and cache hit rates.

src/plugin-handlers/agent-config-handler.ts

@@ -76,6 +76,7 @@ export async function applyAgentConfig(params: {
   const currentModel = params.config.model as string | undefined;
   const disabledSkills = new Set<string>(params.pluginConfig.disabled_skills ?? []);
   const useTaskSystem = params.pluginConfig.experimental?.task_system ?? false;
+  const disableOmoEnv = params.pluginConfig.experimental?.disable_omo_env ?? false;
 
   const builtinAgents = await createBuiltinAgents(
     migratedDisabledAgents,
@@ -90,6 +91,7 @@ export async function applyAgentConfig(params: {
     currentModel,
     disabledSkills,
     useTaskSystem,
+    disableOmoEnv,
   );
 
   const includeClaudeAgents = params.pluginConfig.claude_code?.agents ?? true;