Configure bumpver for Concourse release pipeline

[blarghmatey]

What are the relevant tickets?

N/A

Description (What does it do?)

Adds [tool.bumpver] configuration to pyproject.toml so the Concourse
release pipeline can update the application version automatically on each
release.

The new version format is YYYY.MM.DD.N (e.g., 2026.04.16.1), which
replaces the previous semver-style version strings. This is required by the
Concourse release resource workflow being rolled out in
mitodl/ol-infrastructure#4506.

The VERSION constant in Django settings is updated to the initial release
format version as part of this change.

How can this be tested?

1. With bumpver installed (pip install bumpver), run bumpver update --dry from the repo root and confirm it shows the expected diff with no errors.
2. Check that VERSION in Django settings matches current_version in pyproject.toml.

Additional Context

Part of the Concourse release pipeline modernization — migrating from the Doof
Slack bot to a Concourse-native release workflow using GitHub Issues as
production gates.

[Copilot]

Pull request overview

Adds bumpver configuration so the Concourse release pipeline can automatically bump the app’s release version using a date-based scheme.

Changes:

• Add [tool.bumpver] configuration to pyproject.toml, including file patterns for version replacement.
• Update main/settings.py VERSION constant to the new YYYY.MM.DD.N format.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
pyproject.toml	Adds bumpver config and a file pattern intended to update the Django VERSION string during releases.
main/settings.py	Updates the VERSION constant to the initial date-based release version used by the pipeline.

[github-actions]

OpenAPI Changes

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