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

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src/hooks/keyword-detector/index.ts

@@ -1,5 +1,5 @@
 import type { PluginInput } from "@opencode-ai/plugin"
-import { detectKeywords, detectKeywordsWithType, extractPromptText } from "./detector"
+import { detectKeywordsWithType, extractPromptText } from "./detector"
 import { log } from "../../shared"
 import { injectHookMessage } from "../../features/hook-message-injector"