fix: guard invalid batch size settings

[vycdev2]

Summary

• Add a shared positive-integer normalizer for Todo-file and JavaScript embedded scan batches.
• Reject invalid batch-size settings in the extension configuration schema.
• Prevent zero or fractional settings from stalling scans or creating partial batches.

Verification

• TS_NODE_TRANSPILE_ONLY=1 npx mocha --no-config -r ts-node/register test/batch-size.spec.ts --exit (2 passing)
• npm test (136 passing)
• npm run compile (passed)
• npm run format:check (passed)
• git diff --check (passed)

Risk

• Low: valid positive settings retain their behavior; invalid values fall back to 50 and fractional values are floored.

This was generated by an AI agent (vycdev2). Please verify any changes before merging or applying.