chore: remove dead code - unused imports and variables

- Remove unused import OhMyOpenCodeConfig from src/index.ts
- Remove unused import dirname from src/features/opencode-skill-loader/loader.ts
- Remove unused import detectKeywords from src/hooks/keyword-detector/index.ts
- Remove unused import CliMatch from src/tools/ast-grep/utils.ts
- Prefix unused parameter _original in src/tools/ast-grep/utils.ts

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/index.ts

@@ -53,7 +53,7 @@ import {
 } from "./tools";
 import { BackgroundManager } from "./features/background-agent";
 import { SkillMcpManager } from "./features/skill-mcp-manager";
-import { type OhMyOpenCodeConfig, type HookName } from "./config";
+import { type HookName } from "./config";
 import { log } from "./shared";
 import { loadPluginConfig } from "./plugin-config";
 import { createModelCacheState, getModelLimit } from "./plugin-state";