a shared housekeeping-label convention across CliMA

## Context

From the group-meeting discussion on getting an overview of all issues/PRs across CliMA: org-scoped GitHub search (`org:CliMA state:open label:"bug 🐞"`, etc.) already gives a single cross-repo view — see [`workflow/cross_repo_issue_pr_search.md`](https://github.com/CliMA/DeveloperGuides/blob/main/workflow/cross_repo_issue_pr_search.md) for the query patterns. That view only works if the relevant labels are applied across the org.

## Problem

Labels are not consistent across CliMA repositories. The same concern may be labelled `bug` in one repo, `bug 🐞` in another, and left unlabelled in a third. No single org-scoped query can then find every item in a category, which defeats the cross-repo overview, especially for "housekeeping" tasks.

## Proposal

Adopt a common housekeeping label (optionally: per category), used verbatim by people and bots alike, so one `org:CliMA … label:` query is complete.

Concrete actions:

1. **Agree the canonical label strings** (exact text, including emoji) for the categories that warrant org-wide tracking — e.g. `dependencies`, `release-blocker`.
2. **Apply the labels uniformly** across CliMA repos: create the missing ones; reconcile divergent spellings.
3. **Align bots with the convention.** Dependabot's labels are set per repo in `.github/dependabot.yml`; point its `labels:` at the agreed string:

```yaml
updates:
- package-ecosystem: "github-actions"
directory: "/"
schedule:
interval: "weekly"
labels:
- "dependencies"
```

## Notes

- Once the label strings are settled, update the recipe table in `workflow/cross_repo_issue_pr_search.md` so the documented queries match reality.