Adds README.md to each of the 13 SPM packages (AgentCore, Bus, Config,
DevOverlay, Harness, Keychain, Logging, MCP, Memory, Replay, Shell, Vision,
Voice). Each covers purpose, key public types, deps, consumers, invariants
(pulled from CLAUDE.md + grep-gates + audit findings), test stack, and
notable files. Memory README explicitly marks the package functionally OFF
until vec0.dylib + Ollama models land.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
