refactor(dirs): centralized directory path utilities into @oh-my-pi/pi-utils/dirs module

- Extracted directory path utilities from multiple packages into a centralized '@oh-my-pi/pi-utils/dirs' module.
- Moved 30+ path helper functions (getAgentDir, getConfigRootDir, getPluginsDir, getMCPConfigPath, etc.) from scattered locations into a single shared utility module.
- Consolidated APP_NAME, CONFIG_DIR_NAME, and VERSION constants into the centralized dirs module for reuse across packages.
- Updated 70+ import statements across packages/ai, packages/coding-agent, packages/stats, and packages/tui to use the new centralized module.
- Removed local path construction logic and replaced with utility function calls for improved maintainability and consistency.
- Deleted packages/coding-agent/src/extensibility/plugins/paths.ts as its functions were moved to the centralized dirs module.

packages/coding-agent/src/cli/plugin-cli.ts

@@ -3,8 +3,9 @@
  *
  * Handles `omp plugin <command>` subcommands for plugin lifecycle management.
  */
+
+import { APP_NAME } from "@oh-my-pi/pi-utils/dirs";
 import chalk from "chalk";
-import { APP_NAME } from "../config";
 import { PluginManager, parseSettingValue, validateSetting } from "../extensibility/plugins";
 import { theme } from "../modes/theme/theme";