Single GitHub tab for repos; entries dated and ordered by actual commits

Repository management moved into the GitHub tab — Project repository settings are no longer duplicated across tabs. Repositories are now managed from the single GitHub tab in Project Settings, and the settings form accepts the current repos so configuration is easier to find and update.
Changelog entries reflect real commit times and sources — Entries are now enriched with commit metadata (commit time, short SHA, and repo when available) and the list is sorted by actual commit timestamp (falling back to creation time). Entry cards show the commit date, short SHA and repo owner/name so the feed matches real commit order across linked repositories.

Moved repository management into the GitHub tab of Project Settings so the Repositories section no longer appears duplicated across tabs.frontend

Updated the project header to show either repo_owner/repo_name for single‑repo projects or “N repositories” for multi‑repo projects, and to derive an overall sync status across all linked repos.frontend
Increased the default entries list limit and allowed fetching up to 100 entries to improve list loading for larger projects.backend

Joined entries with commits to return committed_at and SHA, enriched each entry with committed_at, commit_sha_short, repo_owner and repo_name (when known), and sorted entries by committed_at DESC with fallback to created_at.backend
Extended EntryListItem with commit_shas, committed_at, commit_sha_short, repo_owner and repo_name fields so clients can display accurate commit metadata.database

Fixed entry ordering so the changelog list reflects actual commit order across all linked repositories.backend