feat(tools): notify — the first client tool

Desktop notifications are the wave-1 built-in the resident has no
native way to send: the daemon's pushes land in the poll queue, and
this is the program that turns one into an OS notification —
`notify push --title --body [--device]` on the shared plumbing, the
claw's `POST /v1/notifications` on the far end.

The binary is the template for every later client: connection from
the environment the daemon provisions, one contract-headered call,
JSON or error shape, exit code. The e2e test drives the real binary
against a mock claw — a wrong token is a 401 with the code to match,
a consent route is a 403, a good push prints the row — so a packaging
regression cannot pass silently. `skills/` ships the markdown that
teaches the agent the tool exists and what its answers mean.

tools/.gitignore

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