Zero-ceremony operation — one binary, no server, no daemon

dira is invoked from hooks, several times per session, in the latency path of a human waiting for a prompt to return. Every millisecond of cold start and every step of setup is felt directly.

The whole tool must therefore be: one static binary, no runtime to install, no process to keep alive, no port to own, no account to create, and no network call on the happy path. Storage is files in the repo you already have; sync is the git remote you already push to.

Achieved when: `brew install dira && dira init` is the entire onboarding, the binary works with the network unplugged, and `dira brief` returns in well under 100ms on a cold cache.