docs: three documented facts about this repository are no longer true

### Problem

Three pieces of documentation describe machinery or state that does not exist. Each misleads a new contributor — and, increasingly, any coding agent reading them as ground truth.

**1. `.claude/projects/js-to-ts/PROJECT.md` says 219 JavaScript files remain to convert.**
Measured today: **6** `.js`/`.jsx` files across `superset-frontend/src`, `packages` and `plugins`. `src/` is at zero. The migration is done in application code; the playbook describes a finished job.

**2. `docs/developer_docs/contributing/issue-reporting.md` documents an issue lifecycle that does not run.**
It describes a bot marking issues stale after 30 days and closing them 7 days later. There is no stale workflow among the repository's workflows. `.github/stale.yml` still exists and configures probot/stale, which is not installed. The same page documents status labels `needs-triage`, `confirmed`, `in-progress` and `blocked`; none of them exist in the repository's label set.

**3. `LLMS.md` was renamed to `AGENTS.md`, but three docs still reference the old name:**
```
docs/developer_docs/contributing/development-setup.md
docs/developer_docs_versioned_docs/version-6.1.0/contributing/development-setup.md
docs/user_docs_versioned_docs/version-6.0.0/contributing/development.mdx
```

### Proposed change

Correct each to describe what is actually true, or delete the parts describing machinery that no longer exists. Where something is an aspiration rather than a fact, saying so explicitly is enough.

Verified against `master` at `3539c41dab`.

Start with .claude/projects/js-to-ts/PROJECT.md, docs/developer_docs/contributing/issue-reporting.md, .github/stale.yml, LLMS.md, AGENTS.md, and the three listed setup documentation files. Verify the documented file counts, stale workflow and labels against the repository, then update or remove inaccurate statements and replace outdated LLMS.md references; done means the docs match the current repository state.

Written by the indexing model from the issue text.