Regenerate LLM history now uses batch sync so UI and period summaries update

LLM history regeneration now runs the full batch sync and period aggregation — Regenerating history now creates a sync run, fans out commits as batches, and triggers period aggregation automatically so the UI shows active sync status and new changelog period summaries are created when complete.

Fixed regenerate-llm-history so it created a sync_run and set repos to 'processing', causing the UI to immediately show an active sync state.backend
Fixed fan-out to emit commit/batch.received (with syncRunId) through the normal batch pipeline instead of single-commit events so batch coordination works correctly.backend
Fixed batch registration so the system registered batch counts with the sync_run and fired changelog/commits.batch.completed when the final batch finished.database
Fixed lifecycle completion so generate-period-backfill ran inline and finaliseSync set repos back to idle, ensuring period summaries were regenerated and the UI updated.backend
Fixed handling for projects with no linked repos by completing the sync_run and setting repos idle instead of leaving the project stuck.backend

Improved reliability of full-history regeneration so changelog entries and period summaries are generated automatically without a manual resync.frontend