CONTRIBUTING.md says `make hooks` runs `make verify` before you push; the hook only does that for a push to `main`

## What happens

`CONTRIBUTING.md:40-42`, step 2 of "How a change gets in":

> Run `make verify` before you push. [...] `make hooks` installs a pre-push hook that runs it for you.

`.githooks/pre-push` runs the disclosure check on every push, but runs `make verify` only when the remote ref is `refs/heads/main` (lines 44-47 set `gate=yes`; line 80 exits otherwise). The hook's own header comment says it gates pushes to `main` only. `make hooks` prints the same ("runs 'make verify' before a push to main", `Makefile` target `hooks`).

Contributors are told in step 1 to fork and branch, so their pushes go to a feature branch and the hook never runs `make verify` for them.

## Why it matters

A newcomer who follows the document installs the hook, pushes, sees no verify, and reasonably concludes their change passed it. The first they hear of a lint or coverage failure is CI, after a macOS-runner queue.

## How to check

```bash
make hooks
sed -n 40,80p .githooks/pre-push
```

## Acceptance criteria

- `CONTRIBUTING.md` step 2 says what the hook actually does: the disclosure check on every push, `make verify` only on a push to `main`, so contributors should run `make verify` themselves before pushing a branch.
- Nothing else about the hook changes.

## Where to start

- `CONTRIBUTING.md` lines 40-42 only.
- `make docs-audit` checks the paths and links in the file.
- Read [CONTRIBUTING.md](https://github.com/uttrflow/uttrflow-swift/blob/main/CONTRIBUTING.md) first, and say on this issue that you are taking it.
- Before pushing, run `make verify` (with `DEVELOPER_DIR` pointing at Xcode 26.6 or later). It is the same command CI runs.

**Size:** XS, under 30 minutes.

Read CONTRIBUTING.md lines 40-42 and compare them with .githooks/pre-push lines 44-47 and 80, plus the Makefile hooks target. Update only the documented pre-push behavior, then run make docs-audit; done means the instructions distinguish the disclosure check on every push from make verify on pushes to main and tell branch contributors to run make verify themselves.

Written by the indexing model from the issue text.