refactor(opencode-skill-loader): split loader and merger into focused modules

Extract skill loading pipeline into single-responsibility modules:
- skill-discovery.ts, skill-directory-loader.ts, skill-deduplication.ts
- loaded-skill-from-path.ts, loaded-skill-template-extractor.ts
- skill-template-resolver.ts, skill-definition-record.ts
- git-master-template-injection.ts, allowed-tools-parser.ts
- skill-mcp-config.ts, skill-resolution-options.ts
- merger/ directory for skill merging logic

src/features/opencode-skill-loader/skill-deduplication.ts

@@ -0,0 +1,13 @@
+import type { LoadedSkill } from "./types"
+
+export function deduplicateSkillsByName(skills: LoadedSkill[]): LoadedSkill[] {
+  const seen = new Set<string>()
+  const result: LoadedSkill[] = []
+  for (const skill of skills) {
+    if (!seen.has(skill.name)) {
+      seen.add(skill.name)
+      result.push(skill)
+    }
+  }
+  return result
+}