Register the Unity Android OAuth callback at build time #2092

Tracks PR #2089.

Plan

Goal: Make OAuth sign-in on Android return to the app for Unity SDK users. The package currently ships a manifest with a literal appwrite-callback-<YOUR_PROJECT_ID> scheme that can never be filled in when the package is installed from a git URL (read-only), and that manifest also redeclares UnityPlayerActivity with a launcher intent filter that competes with the project's own main manifest.

What changes (PR #2089):

• Remove templates/unity/Assets/Runtime/Core/Plugins/Android/AndroidManifest.xml.twig and its file entry and Android plugin-importer meta handling in src/SDK/Language/Unity.php.
• Add templates/unity/Assets/Editor/AppwriteAndroidManifestProcessor.cs.twig, an IPostGenerateGradleAndroidProject (guarded by UNITY_ANDROID) that reads projectId from every AppwriteConfig asset and appends a VIEW/DEFAULT/BROWSABLE intent filter for appwrite-callback-<projectId> to the Unity activity in the generated Gradle manifest, skipping schemes already declared. Logs guidance when no config with a project ID exists.
• templates/unity/README.md.twig: new "OAuth on Android" section, including the custom main manifest route for clients created in code.
• templates/unity/Assets/Editor/AppwriteSetupWindow.cs.twig: Documentation button opens the SDK README on GitHub instead of sdk.url; Discord button uses sdk.discordUrl and is hidden when unset.
• tests/generation/GenerationTest.php: tests that no AndroidManifest.xml or <YOUR_PROJECT_ID> placeholder ships, that the processor registers the same appwrite-callback- prefix WebAuthComponent waits for, and that the setup window links to the README with no fixed Discord invite.

Remaining steps: None beyond the linked PR; it is the full change. The fix reaches users with the next Unity SDK release generated from sdk-generator.

Done when:

• PR fix(unity): register the Android OAuth callback at build time #2089 is reviewed and merged
• Generation tests pass in CI
• The next Unity SDK release ships without the package manifest and with the build processor