refactor(firebase-ai-logic-basics): split service management from SDK setup and move references

[AustinBenoit]

Summary

• Restructures SKILL.md to separate platform-independent Service Management (CLI provisioning, provider selection, billing, App Check enforcement, Remote Config rollout, monitoring) from SDK Setup & Usage.
• Performs a pure git mv (100% similarity, zero content diff) of the 4 platform setup files into references/sdk/setup/{android,ios,flutter,web}_setup.md and tts_generation.md into references/sdk/capabilities/text_to_speech.md.
• Per-platform setup updates follow in feat(firebase-ai-logic-basics): update Android SDK setup and App Check guide #219 (Android), feat(firebase-ai-logic-basics): update iOS SDK setup and App Check guide #220 (iOS), feat(firebase-ai-logic-basics): update Flutter SDK setup and add App Check guide #221 (Flutter), and feat(firebase-ai-logic-basics): update Web SDK setup and App Check guide #222 (Web).

[gemini-code-assist]

Code Review

This pull request significantly updates and reorganizes the Firebase AI Logic documentation, introducing comprehensive setup guides for Android (Kotlin), iOS (Swift), Flutter (Dart), and Web (JavaScript). It covers essential topics such as backend provisioning, App Check enforcement, and model rollout with Remote Config. The review feedback correctly identifies compilation errors in the iOS setup guide where the App Check provider factories are incorrectly named AppAttestProviderFactory and DeviceCheckProviderFactory instead of AppCheckAppAttestProviderFactory and AppCheckDeviceCheckProviderFactory.

[AustinBenoit]

/gemini review

[gemini-code-assist]

Code Review

This pull request comprehensively updates the Firebase AI Logic skill documentation and platform-specific setup guides for Android, iOS, Flutter, and Web. The changes restructure the core guide into Service Management and SDK Setup sections, detail App Check enforcement (including replay protection and secure debug token handling), and migrate references to the latest SDK versions and entry points. As there are no review comments, I have no feedback to provide.