sync: multi-branch scanning, discovery strategies, UTF-8 fix, curation improvements

- Add multi-branch scanning to discover skills on non-default branches
- Add popular repos and commits search discovery strategies
- Fix UTF-8 encoding sanitization in skill parser
- Add repo_created_at for threshold-based duplicate tie-breaking
- Add indexer tests and vitest config

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

services/indexer/package.json

@@ -9,7 +9,8 @@
     "worker": "tsx src/worker.ts",
     "crawl": "tsx src/crawl.ts",
     "lint": "eslint src/",
-    "typecheck": "tsc --noEmit"
+    "typecheck": "tsc --noEmit",
+    "test": "vitest"
   },
   "dependencies": {
     "@octokit/rest": "^20.0.2",
@@ -26,6 +27,7 @@
     "@types/node": "^20.10.0",
     "tsup": "^8.0.1",
     "tsx": "^4.7.0",
-    "typescript": "^5.3.0"
+    "typescript": "^5.3.0",
+    "vitest": "^1.2.0"
   }
 }