feat(inference): add native Anthropic (Claude) provider

[johnford2002]

Fork merge of the native Anthropic provider. Upstream contribution PR: karakeep-app#2890 (same change, based on upstream/main).

Summary

Adds a first-class Anthropic (Claude) inference provider, selected by ANTHROPIC_API_KEY, using the official @anthropic-ai/sdk Messages API — instead of routing Claude through Anthropic's OpenAI-compatibility endpoint (which ignores strict/json_schema enforcement, so structured tagging output isn't guaranteed).

What it does

• New AnthropicInferenceClient in packages/shared/inference.ts; selected in InferenceClientFactory.build() when ANTHROPIC_API_KEY is set (precedence: OpenAI → Anthropic → Ollama).
• Text + image inference for auto-tagging and summarization, with native Structured Outputs (output_config.format json_schema) for guaranteed schema conformance.
• Defaults to claude-haiku-4-5 (override via INFERENCE_TEXT_MODEL / INFERENCE_IMAGE_MODEL).
• New env vars ANTHROPIC_API_KEY + optional ANTHROPIC_BASE_URL; docs updated. Purely additive.

Limitations

• No embeddings (Anthropic has none) — generateEmbeddingFromText throws a clear error; semantic search needs a separate embedding provider.

Test plan

• packages/shared/inference.test.ts (8 tests) green; pnpm format/lint/typecheck/build pass; @karakeep/shared suite (111) green.

🤖 Generated with Claude Code