fix(sync): batch inserts + normalize nulls to avoid SQLite param mismatch

- Batch repository inserts with dynamic sizing under SQLite 999-param limit
- Normalize undefined → null to keep multi-row insert shapes consistent
- De-duplicate owned + starred repos by fullName (prefer starred variant)
- Enforce uniqueness via (user_id, full_name) + onConflictDoNothing
- Handle starred name collisions (suffix/prefix) across mirror + metadata
- Add repo-utils helpers + tests; guard Octokit.plugin in tests
- Remove manual unique index from entrypoint; rely on drizzle-kit migrations

src/lib/github.ts

@@ -18,8 +18,11 @@ if (process.env.NODE_ENV !== "test") {
   }
 }
 
-// Extend Octokit with throttling plugin
-const MyOctokit = Octokit.plugin(throttling);
+// Extend Octokit with throttling plugin when available (tests may stub Octokit)
+// Fallback to base Octokit if .plugin is not present
+const MyOctokit: any = (Octokit as any)?.plugin?.call
+  ? (Octokit as any).plugin(throttling)
+  : Octokit as any;
 
 /**
  * Creates an authenticated Octokit instance with rate limit tracking and throttling