Closes DOCS-1390
## Problem
Sentry [DOCS-AA](https://supabase.sentry.io/issues/7727380816/) reports
`NotAllowedError: Failed to execute 'write' on 'Clipboard': Write
permission denied.` as an unhandled promise rejection.
The error names `write`, not `writeText`, which places it in the
`ClipboardItem` branch of `copyToClipboard`. That branch has two
problems:
- The write runs inside a `setTimeout`, so the surrounding `try/catch`
has already returned by the time it executes. A denied write routes to
the promise's `reject`.
- No caller attaches a `catch`. All call sites either fire-and-forget or
`await` inside an async handler with no `try/catch`, so the rejection
surfaces as an unhandled rejection.
The user-visible effect is worse than the Sentry noise. On that branch
the copy fails with no feedback at all, because the `toast.error` in the
outer `catch` is unreachable from inside the `setTimeout`. The
`writeText` branch does show the toast, so the two paths disagree.
The issue is filed against auth docs, where it surfaced, but the fix
belongs in `packages/ui`. The same branch runs in Studio and www.
## Solution
- Handle the failure inside the `setTimeout`, where it happens: report
it and resolve.
- `copyToClipboard` no longer rejects on either path, matching what the
`writeText` branch already did. No caller relied on rejection.
- Add regression tests for a denied write on both branches.
## Manual testing
1. Run the unit tests. Four `copyToClipboard` cases pass, including the
two new denial cases.
```
pnpm --filter studio exec vitest run lib/helpers.test.ts -t
copyToClipboard
```
2. Confirm the new test is a real guard. Revert `clipboard.ts` and
rerun. The write case fails with `promise rejected ... instead of
resolving`.
3. Confirm the ratchet is unchanged.
```
pnpm --filter studio run lint:ratchet
```
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Bug Fixes**
* Clipboard write failures now display an error notification instead of
causing an unhandled rejection.
* Copy operations resolve consistently when clipboard access is denied
or unavailable, including Safari clipboard support.
* Failed copy attempts no longer trigger completion callbacks,
preventing misleading success behavior.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
Miranda Limonczenko
91b7df64c2