refactor(CardTemplateEditor): wire ViewModel to Activity

[xenonnn4w]

Purpose / Description/ Approch

Wire the CardTemplateEditorViewModel to CardTemplateEditor Activity.

• Add viewModel by viewModels<CardTemplateEditorViewModel>()
• Setup state collection using lifecycleScope.launch { repeatOnLifecycle(STARTED) }
• Handle state changes (shouldFinish, error, message)
• Wire tab selection to update ViewModel state

Links without closing (Part of)

• Migrate Card Template Editor to Rust backend for atomic notetype updates #19956

Based on

• refactor(CardTemplateEditor): add ViewModel + State infrastructure #20103

How Has This Been Tested?

No regressions obtained, and all TemplateEditorViewModelTest passes.

Checklist

Please, go through these checks before submitting the PR.

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner

[xenonnn4w]

The when block for UserMessage includes SaveSuccess and CantAddTemplateToDynamic with generic placeholder strings (dialog_ok, multimedia_editor_something_wrong). Nothing in the ViewModel currently triggers these messages. Will be updated follow up PR.