Simplified scheduling, non‑destructive history regeneration, and smoother project setup

Simplified publishing schedule with non‑destructive archive/restore regeneration — Publishing was unified around frequency-based aggregation (daily/weekly/monthly). Changing schedule now archives existing period summaries and can restore or regenerate history in the background so you can switch frequencies without losing approval state or edits.
Faster, clearer project onboarding with multi‑repo setup and real‑time impact estimates — New multi-repo project creation, slug availability checks and suggestions, and a history impact estimator let you see how many commits and period entries will be generated before processing repository history.

Unified publishing model to always ingest commits and group them by frequency (daily/weekly/monthly) rather than relying on multiple trigger types.backend
Made schedule changes safer: period summaries are now soft-archived and can be restored or regenerated on demand, preserving publish/draft state.backend
Added monthly boundary option (first_day / last_day) and expanded schedule controls (frequency, time, timezone, week start day, month boundary).frontend
Improved project creation UX: select multiple repositories, choose tracked branch per repo, and persist selections when navigating the wizard.frontend
Added migration choices for schedule, LLM, and repo changes so you can choose to apply changes forward‑only or regenerate history from inception.frontend
Added unsaved-changes protection on settings tabs and per-tab dirty tracking to avoid accidental navigation loss.frontend

Added POST /v1/github/history-estimate and a /api/github/history-estimate proxy to compute commit counts and estimated period entry counts across one or more repos/branches.backend
Added /api/projects/slug endpoint and client-side slug validation with inline suggestions and auto-apply behavior during project creation.frontend
Added events for background flows: history.backfill.requested now drives archive/restore/regeneration and a new changelog/llm.regeneration.requested event triggers full LLM reprocessing of commit history.integrations
Project settings API now accepts migration intents so UI choices (forward_only vs regenerate_history) are honored by background jobs.backend

Added archived_at column to changelog_entries and an index that excludes archived rows so period entries can be soft‑archived and efficiently excluded from public views.database
Repository code updated to archive/unarchive period entries, detect archived entries, and delete commit entries for LLM regeneration workflows.backend

Updated changelog and added tests for settings schemas, migration dialog copy, slug validation, and archive/unarchive repository behaviours.