Improve Claude Code plugin init flow

[wayyoungboy]

Summary

• align Claude Code plugin init around ensuring a PowerMem backend and writing POWERMEM_BASE_URL for hooks
• support ANTHROPIC_API_KEY and ANTHROPIC_AUTH_TOKEN + ANTHROPIC_BASE_URL initialization paths with source logging
• keep environment-derived credentials isolated from settings.json provider/base URL fallback
• record and reuse managed powermem-server pid/runtime URL, add CN pip mirror detection, and show the dashboard URL after startup
• update plugin setup/status/stop docs and flow diagram

Validation

• source .venv/bin/activate && sh -n apps/claude-code-plugin/scripts/init.sh
• source .venv/bin/activate && python -m compileall -q apps/claude-code-plugin/scripts
• source .venv/bin/activate && pytest tests/unit/test_anthropic.py tests/unit/server/test_search_score_threshold.py
• source .venv/bin/activate && pytest (completed locally; current local baseline is not green: 666 passed, 109 failed, 91 errors, 9 skipped)