[aclark4life]

INTPYTHON-1126

Changes in this PR

• Genericize the branch relationship summary table: no real PR numbers, so it no longer needs updating each release cycle.
• Document the daily upstream-sync workflow in the Django fork (triggers, updated branches, conflict/push-rejected issues).
• Document the CI re-trigger after a fork-branch force-push: the three ci_rerun kinds, where the mapping is configured, and links to the workflow and retrigger-ci action sources.
• Add a diagram of how a fork rebase force-push re-triggers backend CI.

Test Plan

• Built the docs with Sphinx (-q -W passes).

Checklist

Checklist for Author

• Did you update the changelog (if necessary)?
• Is the intention of the code captured in relevant tests?
• If there are new TODOs, has a related JIRA ticket been created?

Checklist for Reviewer

• Does the title of the PR reference a JIRA Ticket?
• Do you fully understand the implementation? (Would you be comfortable explaining how this code works to someone else?)
• Have you checked for spelling & grammar errors?
• Is all relevant documentation (README or docstring) updated?