fix(branding): point the product license link at HEAD, not the missing main branch

product.overlay.json set licenseUrl/serverLicenseUrl to
github.com/levelcodeai/levelcode/blob/main/LICENSE, but there is no `main` branch
— the default is `develop` — so the license link baked into the app's About /
license metadata 404'd. Use /blob/HEAD/LICENSE: GitHub resolves HEAD to whatever
the default branch is, so it works on develop today and survives a future rename
to main.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: ndemianc

branding/product.overlay.json

@@ -26,8 +26,8 @@
   "_syncComment": "LevelCode Sync (built-in Settings Sync + the `levelcode` auth provider from extensions/levelcode-sync) was REMOVED for now — the managed sync host isn't built and it duplicated the LevelCode Cloud sign-in. Removed at source: the levelcode-sync extension, this configurationSync.store block, and the Welcome 'Sync' step. Re-add when the managed sync host ships.",
 
   "licenseName": "MIT",
-  "licenseUrl": "https://github.com/levelcodeai/levelcode/blob/main/LICENSE",
-  "serverLicenseUrl": "https://github.com/levelcodeai/levelcode/blob/main/LICENSE",
+  "licenseUrl": "https://github.com/levelcodeai/levelcode/blob/HEAD/LICENSE",
+  "serverLicenseUrl": "https://github.com/levelcodeai/levelcode/blob/HEAD/LICENSE",
   "reportIssueUrl": "https://github.com/levelcodeai/levelcode/issues/new",
   "win32ShellNameShort": "LevelCode",
   "crashReporter": { "companyName": "SystemU", "productName": "LevelCode" },