CHANGELOG has no link definition for the [2026.9.14] heading

## What happens

`CHANGELOG.md:12` has the heading `## [2026.9.14] — 2026-09-14`, written as a Markdown reference link, but the link definitions at the foot of the file (lines 456-460) only cover `[Unreleased]`, `[0.5.0]`, `[0.4.0]`, `[0.3.0]` and `[0.2.2]`. The definition was left out on purpose, because the link checker would have failed on a release page that did not exist yet.

The release now exists: tag `v2026.9.14` is published on this repository's Releases page.

## Why it matters

The newest heading is the one people click, and today it renders as plain bracketed text.

## How to check

Search `CHANGELOG.md` for `[2026.9.14]:`. There is no match.

## Acceptance criteria

- A `[2026.9.14]: https://github.com/uttrflow/uttrflow-swift/releases/tag/v2026.9.14` definition is added in the block at the foot, in date order with the others.
- `make verify` passes, including the link check (`lychee.toml` configures it).

## Where to start

- `CHANGELOG.md` (line 12 and lines 456-460)
- Tests to extend: none needed; the link checker in `make verify` is the test.
- Before pushing, run `make verify` (export DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer first). It is the same command CI runs, and it enforces the 95% coverage floor per module.
- Read [CONTRIBUTING.md](https://github.com/uttrflow/uttrflow-swift/blob/main/CONTRIBUTING.md) first, and say on this issue that you are taking it.

**Size:** XS, under an hour.

Read CONTRIBUTING.md first, then open CHANGELOG.md at line 12 and the link-definition block around lines 456-460. Add the missing release definition in date order, then run `export DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer` followed by `make verify`; done means the link checker passes and the new release heading resolves correctly.

Written by the indexing model from the issue text.