docs: add video embeds and unify cookbook naming (#123)

* docs: expand GeneralUpdate.Tools Mobile packaging documentation

- Add technical internals: format detection (APK vs AAB), AXML binary
  parsing (StringPool, StartElement chunks, versionCode extraction),
  project build pipeline (CsprojParser, dotnet publish, artifact locate)
- Add upload form field mapping table with data sources and examples
- Add upload service configuration details (endpoint, auth, DPAPI)
- Add 5 mobile-specific FAQ entries
- Add missing Mobile section to zh-Hans i18n copy
- Sync all changes to English i18n

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

* docs: rename 'Quickstart' to 'Cookbook' for Avalonia/Maui Android guides

- Avalonia Android: 快速入门 → 实战手册, Quickstart → Cookbook
- MAUI Android: 快速入门 → 实战手册, Quickstart → Cookbook

Aligns naming convention with Beginner cookbook.

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

* docs: add Bilibili demo videos to cookbook pages

- GeneralUpdate.Tools Mobile: Android packaging demo (BV1ctJF6XEJs)
- Avalonia Android cookbook: upgrade demo (BV1HtJF6XET3)
- MAUI Android cookbook: upgrade demo (BV1ntJF6XEvG)

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

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Co-authored-by: Claude <noreply@anthropic.com>

Author: JusterZhu