refactor(coding-agent/cli): restructured CLI help rendering into dedicated oclif-help module

- Extracted custom help class implementation into dedicated oclif-help.ts module to centralize CLI help rendering logic.
- Refactored printHelp() function to delegate detailed help output to oclif's Help class, reducing code duplication and complexity.
- Extracted getExtraHelpText() function to isolate environment variables help section for reuse across help implementations.

packages/coding-agent/package.json

@@ -13,6 +13,7 @@
 	"oclif": {
 		"bin": "omp",
 		"commands": "./src/commands",
+		"helpClass": "./src/cli/oclif-help.ts",
 		"plugins": [
 			"@oclif/plugin-autocomplete"
 		]