Fix crash when hook entries have no matcher (#160)

Claude Code allows hook entries without a `matcher` field (e.g.,
SessionStart and SubagentStop hooks don't need one). The OpenCode
converter assumed `matcher.matcher` was always present, causing
"undefined is not an object (evaluating 'matcher.matcher.split')"
when converting plugins with matcher-less hooks.

Make `matcher` optional in the type and guard all accesses.

src/types/claude.ts

@@ -79,7 +79,7 @@ export type ClaudeHookAgent = {
 export type ClaudeHookEntry = ClaudeHookCommand | ClaudeHookPrompt | ClaudeHookAgent
 
 export type ClaudeHookMatcher = {
-  matcher: string
+  matcher?: string
   hooks: ClaudeHookEntry[]
 }