ER: Use static-issue-nums Agenda Issue definition in GHA scripts

### Emergent Requirement - Problem
We should update the GHA helper-script `create-new-issue.js` to import the current Agenda Issue number from `static-issue-nums.json` rather than using a local hard-coded constant, so that only `static-issue-nums.json` needs to be updated when the Agenda Issue number changes.

### Issue you discovered this emergent requirement in
- #8451

### Date discovered
2026-02-05

### Did you have to do something temporarily
- [ ] YES
- [x] NO

### Who was involved
@myronchen-git
@ryanfkeller

### What happens if this is not addressed
Each year when the Agenda Issue number is updated, the Agenda Issue number will need to be updated in multiple locations.

### Resources
- Loading JSON files in CJS: [https://blog.logrocket.com/reading-writing-json-files-node-js-complete-tutorial/](https://blog.logrocket.com/reading-writing-json-files-node-js-complete-tutorial/)

### Recommended Action Items
- [ ] Make a new issue
- [ ] Discuss with team
- [ ] Let a Team Lead know

### Potential solutions [draft]
1. Require the `static-issue-nums.json` in `create-new-issue.js` with the following :
```javascript
const STATIC_ISSUE_NUMS = require("../../utils/_data/static-issue-nums.json");
```
2. Update the `postComment()` call currently using `AGENDA_ISSUE_NUM` to instead use `STATIC_ISSUE_NUMS.AGENDA`