feat(kafka): add opt-in workflow micro-batching

[xiami762]

Summary

• add opt-in Kafka micro-batching with configurable max records and wait window
• deliver decoded batches through the existing workflow input key without exposing Kafka metadata
• use manual offset commits after successful workflow execution while preserving legacy single-record auto-commit defaults
• persist batch settings across trigger compatibility paths and expose them in the workflow integration UI

Compatibility

• batchMaxRecords defaults to 1, preserving the existing single-record behavior
• workflows require no definition changes unless they opt in and consume list payloads

Verification

• uv run ruff check on modified Python files
• 67 related backend tests passed
• npm run build passed