chore: keep the design-partner names out of merge commits

[suchapalaver]

Context

The repository is going public (Epic #561). One active feature branch is named after the design partner and carries commits whose messages name the partner.

Current state

• Remote branch feat/ford_demo exists and is active (most recent commit ~1 day old at time of writing; ~30 commits not yet on main; no PR open yet).
• Both the branch name and several of its commit messages contain the partner's name. On a public repo, branch names and commit messages are visible.

Why it matters

The metadata and tree were scrubbed of the partner's name, but this branch would reintroduce it into the public surface (branch list + commit history) the moment the repo goes public. It must be handled by the branch owner so their in-progress work and local tracking are not disrupted.

Acceptance criteria

• The branch is renamed to a generic name (e.g. feat/grafana-incident-demo) by its owner, and stale remote refs are cleaned up.
• When the work merges, the PR title and the squash-merge commit subject use generic language so the partner's name does not land on main.
• No partner name remains in the public branch list or in any commit that reaches main via this work.

Suggested approach

Branch owner renames locally and re-pushes (git branch -m, push new, delete old remote), so their tracking stays intact — do not rename someone else's active branch for them. Because merges here are squash-merges, the partner name can be kept off main entirely by setting a generic squash subject at merge time; no history rewrite is needed.

Out of scope

The commit messages already on main and in refs/pull/* (accepted residue per Epic #561).

Part of #561.