v0.3.1 - Shared-memory docs and Gemini CLI rollout

Patch release for cross-client continuity documentation and Gemini CLI support.\n\nHighlights:\n- document shared local project memory handoffs across Codex and Gemini CLI\n- add Gemini CLI client integration guidance, smoke coverage, and ready fixture\n- update live client tiers so server_info/self_test include Gemini CLI\n- refresh release-facing install/version references to v0.3.1