[Feature]: Support multiple AI service providers (beyond Gemini)

[MRAKS05]

Problem

The app currently only supports Google Gemini Flash Lite (gemini-flash-lite-latest) for AI-powered browser classification (GeminiClient.kt, line 52). This creates a single point of failure:

• If Gemini is down or rate-limited, detection falls back to the hardcoded browser list (BrowserDatabase.kt — 52 known packages)
• Users must have a Gemini API key, which requires a Google account and enabling billing
• No alternative providers for users who prefer different services or face regional restrictions

Proposed Solution

Add support for multiple AI service providers, prioritizing free-tier or low-cost options with free model access, then build a unified UI for provider/model selection.

Candidate Providers

Provider	Free Tier	Notes
Groq	Yes (Llama 3 / Mixtral)	Very fast inference, free tier available
OpenRouter	Varies	Single API key gateway to many models
Together AI	Free credits	Multiple open-source models
Hugging Face Inference	Free tier	Community models
OpenAI	No	GPT-4o mini, reliable

Architecture Requirements

• Abstract AiService interface: Common contract (classifyApp(packageName, metadata): ClassificationResult) so the rest of the app (BrowserDetector.kt, LogsScreen.kt) is provider-agnostic
• Per-provider adapter: Each provider implements the interface with its own API client, prompt format, and error handling
• Fallback chain: Try primary provider first; if it fails, fall through to secondary, then tertiary, then local list
• Provider status tracking: Per-provider daily quota tracking (currently only Gemini has SettingsManager.tryUseGeminiApi() with a 20/day limit)

UI Requirements

• Provider selection screen: New section in Settings to add/configure providers
• Model picker: Per-provider model selection dropdown
• API key management: Per-provider key input with masked fields (similar to current Gemini key input at SettingsScreen.kt lines 67-97)
• Active provider ordering: Drag-to-reorder priority list
• Status indicators: Show which providers are configured, which are reachable