feat(dotcom): link top-left logo to tldraw.dev (tldraw#8938)

In order to harden the symbiosis between tldraw.com and tldraw.dev
(tldraw#8871), this PR repoints the top-left logo on the anonymous tldraw.com
editor panel from an in-app `Link to="/"` to an external anchor at
`https://tldraw.dev`. The new anchor uses `target="_blank"` with
`rel="noopener noreferrer"`, an `aria-label` for screen readers (the
logo is image-only), and UTM params
(`utm_source=dotcom&utm_medium=organic&utm_campaign=top-left-logo`)
matching the existing sidebar dot.dev link and overlay CTA conventions.

The change applies to all three render contexts of the anonymous panel
via the shared `TlaEditorTopLeftPanelAnonymous` component: root
tldraw.com, anonymous guest on someone else's file, and logged-out
viewer of a published file. The signed-in panel is unaffected (its
top-left has no clickable logo; the sidebar provides file navigation).

### Things considered

- **Loss of in-app "home" navigation for anon users.** The original
`Link to="/"` was the only way for an anonymous viewer of a
shared/published file to return to tldraw.com. In practice this is not a
real loss: anon users on a shared/published file have no file index to
return to, and the browser back button is unchanged. Signed-in users
navigate the file list via the sidebar (`TlaSidebar`), which is
untouched.
- **Optional follow-ups not included** to keep scope tight: a
`useTldrawAppUiEvents` click-tracking hook, and a regression e2e spec
mirroring `apps/dotcom/client/e2e/tests/sidebar-dotdev-link.spec.ts` for
the top-left logo. Happy to follow up in separate PRs.

Closes tldraw#8871

### Change type

- [x] `improvement`

### Test plan

1. Open tldraw.com in a logged-out browser (or any anonymous context:
shared file, published file).
2. Click the tldraw logo in the top-left of the editor.
3. Confirm a new tab opens at
`https://tldraw.dev?utm_source=dotcom&utm_medium=organic&utm_campaign=top-left-logo`.
4. Confirm the original tab stays on tldraw.com.
5. Inspect the logo's `<a>` element: `target="_blank"`, `rel="noopener
noreferrer"`, `aria-label="tldraw.dev"`.

- [ ] Unit tests
- [ ] End to end tests

### Release notes

- Link the top-left tldraw logo on tldraw.com to tldraw.dev.

### Code changes

| Section | LOC change |
| --- | --- |
| Apps | +9 / -3 |

Co-authored-by: Jessica Claire Edwards <jessica@tldraw.com>

Author: jsscclr

apps/dotcom/client/src/tla/components/TlaEditor/TlaEditorTopLeftPanel.tsx

@@ -1,6 +1,6 @@
 import classNames from 'classnames'
 import { useCallback, useEffect, useRef, useState } from 'react'
-import { Link, useParams } from 'react-router-dom'
+import { useParams } from 'react-router-dom'
 import {
 	AccessibilityMenu,
 	ColorSchemeMenu,
@@ -106,9 +106,15 @@ export function TlaEditorTopLeftPanelAnonymous() {
 
 	return (
 		<>
-			<Link to="/" className={styles.topLeftOfflineLogo}>
+			<a
+				href="https://tldraw.dev?utm_source=dotcom&utm_medium=organic&utm_campaign=top-left-logo"
+				target="_blank"
+				rel="noopener noreferrer"
+				aria-label="tldraw.dev"
+				className={styles.topLeftOfflineLogo}
+			>
 				<TlaLogo data-testid="tla-top-left-logo-icon" />
-			</Link>
+			</a>
 			{anonFileName && (
 				<>
 					<span