Add Anthropic/Claude as an AI provider

[akuligowski9]

Summary

Add Claude (Anthropic) as a fourth AI provider option alongside Gemini, OpenAI, and Ollama.

Context

The AiSummarizer service already supports three providers via a callProvider() dispatch method. Each provider has its own private method (summarizeItemsWithGemini, summarizeItemsWithOpenAI, summarizeItemsWithOllama) that builds the HTTP request, parses the response, and returns enriched items. Adding a new provider means following this exact pattern.

What to do

1. Add env vars to config/ai.php: ANTHROPIC_API_KEY, DIGEST_AI_MODEL_ANTHROPIC (default: claude-sonnet-4-5-20250929)
2. Add summarizeItemsWithAnthropic() to AiSummarizer — use the Messages API with response_format: { type: "json" }
3. Add 'anthropic' case to callProvider()
4. Add env vars to .env.example with comments
5. Add tests: happy path + missing API key placeholder (follow existing test pattern in AiSummarizerTest)

Files to modify

• config/ai.php
• app/Services/AiSummarizer.php
• .env.example
• tests/Unit/AiSummarizerTest.php

Reference

Look at summarizeItemsWithOpenAI() as the closest pattern — Anthropic's Messages API is similar (JSON body, bearer token, structured response).