Fix: Rename app.ts to App.ts for correct casing

[Copilot]

The TypeScript file was named app.ts (lowercase) while all references used App.ts (capital A).

Changes

• Renamed /src/Client/Bit.TemplatePlayground.Client.Core/Scripts/app.ts → App.ts

This aligns the file name with:

• Import statement: import { App } from './App'; in index.ts
• Documentation references in .docs/11- TypeScript, Build Process & JavaScript Interop.md
• Code comments in AppJsBridge.razor and AppJsBridge.razor.cs

Original prompt

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This section details on the original issue you should resolve

<issue_title>App.ts casing issue in the project</issue_title>
<issue_description>It should be App.ts, not app.ts</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes App.ts casing issue in the project #90

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