fix(desktop): grant clipboard permissions in preview browser

[nsxdavid]

Fixes #3738

What Changed

• Added "clipboard-sanitized-write" to the preview browser session's permission request allowlist (apps/desktop/src/preview/BrowserSession.ts)
• Installed a permission check handler on the same session; Electron consults this synchronous handler for clipboard APIs and none existed
• Both handlers share one hoisted allowlist constant, with the legacy "clipboard-write" name included only where the request handler can receive it
• Unit test covering both handlers (clipboard permissions granted, unrelated permissions denied), plus the missing mock method in the existing test setup

Why

The preview browser's permission handler allows "clipboard-write", but the permission Chromium actually requests for navigator.clipboard.writeText() is "clipboard-sanitized-write". The grant never matches, and since Electron shows no permission prompts, every clipboard write from a previewed page is silently denied. Copy buttons in previewed apps fail with:

Cannot read properties of undefined (reading 'writeText')  (http pages)
NotAllowedError                                             (https pages)

The same pages work in Chrome, which prompts the user and remembers the grant.

Validation

• Reproduced against a Vite dev app in the preview browser: copy button failed before the change, works after
• Verified in a local Windows build (0.0.28) of the desktop app
• vp test apps/desktop/src/preview/BrowserSession.test.ts passes (6 tests)
• vp run typecheck clean for @t3tools/desktop

Checklist

• This PR is small and focused (+55/-2, one concern)
• I explained what changed and why
• No UI change; behavior fix only

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Note

Low Risk
Scoped to desktop preview session permission handlers; no auth or data-path changes, with unit test coverage for grant/deny behavior.

Overview
Fixes preview pages where navigator.clipboard.writeText() was denied because Chromium requests clipboard-sanitized-write, while the preview Electron session only allowed the legacy clipboard-write name on the async request handler.

BrowserSession now centralizes permission allowlists and registers both setPermissionRequestHandler (includes legacy clipboard-write) and a new setPermissionCheckHandler (the sync path Electron uses for clipboard APIs), granting clipboard-read, clipboard-sanitized-write, plus existing notifications / geolocation, while denying unrelated permissions. Tests assert both handlers grant clipboard permissions and reject others.

^{Reviewed by Cursor Bugbot for commit 3063928. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Grant clipboard permissions in the preview browser session

• Adds PERMISSION_REQUEST_ALLOWLIST and PERMISSION_CHECK_ALLOWLIST constants in BrowserSession.ts to centralize permission decisions.
• Installs a setPermissionCheckHandler on sessions created via BrowserSession.make, allowing clipboard-read, clipboard-sanitized-write, notifications, and geolocation.
• Legacy clipboard-write is allowed on permission requests but not on permission checks; all other permissions (e.g. midi) are denied in both handlers.

^{Macroscope summarized 3063928.}

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Approvability

Verdict: Needs human review

This change modifies permission handling for the preview browser, granting clipboard permissions to previewed content. Permission-related changes are security-adjacent and warrant human review, especially from someone familiar with the preview browser security model.

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