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/config/schema/experimental.ts

@@ -15,6 +15,8 @@ export const ExperimentalConfigSchema = z.object({
   plugin_load_timeout_ms: z.number().min(1000).optional(),
   /** Wrap hook creation in try/catch to prevent one failing hook from crashing the plugin (default: true at call site) */
   safe_hook_creation: z.boolean().optional(),
+  /** Disable the OhMyOpenCode environment setup (experimental) */
+  disable_omo_env: z.boolean().optional(),
   /** Enable hashline_edit tool for improved file editing with hash-based line anchors */
   hashline_edit: z.boolean().optional(),
 })