personal memory agent

refactor(providers/google): port cogitate to google-genai SDK master

Move Google cogitate from a Gemini CLI subprocess to the google-genai SDK so tool calls, policy checks, and history are owned in-process. This closes the casual-installer gap by removing the separate gemini binary requirement. The cutover intentionally starts existing Google cogitate sessions fresh once, then persists SDK history under the journal cache. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>