[Feature]: Auto-commit background task

Parent PRD

#254

What to build

A configurable auto-commit mode that batches uncommitted YAML changes and pushes them periodically.

Backend:

• New settings: GIT_AUTO_COMMIT: bool = False and GIT_AUTO_COMMIT_INTERVAL: int = 60 (seconds), persisted in DB and loadable from env vars.
• Background asyncio task that runs on a timer: checks for uncommitted changes via GitService, commits with a summary message, pushes.
• Commit message format: "Ontos auto-sync: {N} files changed ({summary}) at {timestamp}", where summary lists entity types (e.g., "2 contracts, 1 product").
• Task is started/stopped when the setting changes at runtime.
• Auto-commit is paused during sync_all() to avoid partial commits.

Frontend:

• Auto-commit toggle and interval input on the Delivery settings page (visible when indirect mode is expanded).
• Settings saved alongside other delivery mode settings.

Unit test: Mock GitService and timer. Assert commit is called after interval when changes exist. Assert no commit when no changes.

Acceptance criteria

• GIT_AUTO_COMMIT and GIT_AUTO_COMMIT_INTERVAL settings in config, persisted in DB
• Background task commits+pushes on the configured interval when changes exist
• No commit when there are no changes
• Task starts/stops when setting is toggled at runtime
• Auto-commit paused during sync_all()
• Commit messages summarize what changed
• Auto-commit toggle + interval input on delivery settings page
• Unit test for timer/batching logic

Blocked by

• Blocked by #257 (pull-before-push — auto-commit uses commit_and_push which must pull first)

User stories addressed

• User story 5 (toggle between manual and auto-commit)
• User story 6 (configurable auto-commit interval)
• User story 16 (auto-commit messages summarize changes)

Start by reviewing the configuration and database settings flow, the GitService entry points, sync_all(), and the Delivery settings page. Check the dependency on #257 before implementing the timer and runtime lifecycle. Done means persisted settings, correct commit and push behavior only when changes exist, pause behavior during sync_all(), summarized messages, UI controls, and the requested unit test.