feat(llm): Add Claude model provider integration (#177)

[Nsuccess]

Summary

Implements Anthropic Claude as an LLM provider for MemU, enabling chat completions and vision capabilities using Claude models including the latest Opus 4.5.

Changes

New Files

• src/memu/llm/backends/claude.py - ClaudeLLMBackend for HTTP client
• src/memu/llm/claude_sdk.py - ClaudeSDKClient for SDK-based usage
• docs/claude-provider.md - Setup and usage documentation
• tests/test_claude.py - 19 unit tests

Modified Files

• src/memu/llm/backends/__init__.py - Export ClaudeLLMBackend
• src/memu/llm/http_client.py - Register Claude backend, handle auth headers

Implementation

• Proper Claude API format (system as top-level param, content blocks)
• Claude-specific auth headers (x-api-key, anthropic-version)
• Vision support with base64 image format
• Clear documentation on limitations (no embeddings, no transcription)

Supported Models

• claude-opus-4-5-20251124 - Opus 4.5 (default, most intelligent)
• claude-opus-4-20250514 - Opus 4
• claude-sonnet-4-5-20250929 - Sonnet 4.5
• claude-sonnet-4-20250514 - Sonnet 4
• claude-haiku-4-5-20251015 - Haiku 4.5

Tests

All 19 tests passing.

Closes #177

[Jununn]

Hi, the build for this PR is not passing yet. Please make the necessary updates, and we’ll review again after that. Thanks! @Nsuccess

[Nsuccess]

Hi, the build for this PR is not passing yet. Please make the necessary updates, and we’ll review again after that. Thanks! @Nsuccess

Hi @Jununn
I've pushed the fixes for the trailing whitespace and formatting issues that were causing the CI to fail. The changes include:

Fixes:

Removed all trailing whitespace from claude_sdk.py, backends/claude.py, and test_claude.py
Fixed blank line formatting to comply with ruff
Added:

examples/example_claude_provider.py

• End-to-end runnable example demonstrating the full workflow (memorize → retrieve)
  Updated docs/claude-provider.md with environment variable setup and example reference
  The workflow is currently awaiting approval to run. Could you please review it when you get a chance? Thanks