Fix plugin defaults and Hermes install discovery

[ethanj]

Summary

Fix two user-facing plugin issues that affected fresh installs and local setup.

• Claude Code now works in local mode without requiring pre-set ATOMICMEMORY_* environment variables.
• Hermes now installs the AtomicMemory provider into the path Hermes scans for user-installed memory providers.

Changes

Claude Code

• Default unset MCP environment values cleanly so local-mode defaults apply.
• Default lifecycle hook capture level to balanced.
• Honor ATOMICMEMORY_API_URL and ATOMICMEMORY_API_KEY in lifecycle hooks.
• Send Bearer auth headers from hook HTTP calls when an API key is configured.
• Update docs to describe zero-config local mode and hosted overrides.
• Add regression tests for env defaults, hosted URL overrides, and auth header behavior.

Hermes

• Install the provider at $HERMES_HOME/plugins/atomicmemory.
• Remove the previous user-install path under $HERMES_HOME/plugins/memory/atomicmemory.
• Update install, source-dev, and troubleshooting docs.
• Add regression coverage for the installer’s default target path.