docs: SPA pattern noted, todo cleared; harness-base git config mkDefault

programs.git.config.user.{name,email} in harness-base.nix now mkDefault
so the per-agent applied flake's override merges without mkForce.

TODO.md

@@ -30,15 +30,6 @@ Pick anything from here when relevant. Cross-cutting design notes live in
   only see them by watching the live panel of the agent that sent them.
 - **Per-agent UI substance.** Show last N inbox messages, last turn timing,
   link back to dashboard.
-- **Static-asset SPA-style web UI.** Move toward: `index.html` is static,
-  CSS/JS is static, all dynamic state is fetched over SSE / JSON endpoints.
-  Currently the index HTML is server-rendered with state-dependent
-  fragments inlined; the live event stream + async forms are already SSE /
-  fetch. Goal is a cleaner split so the UI is one HTML file + JS app +
-  small JSON API.
-- **Background JS refresh on the live panel.** Already there for sends;
-  any remaining places that reload the whole page should switch to fetch +
-  partial updates.
 - **xterm.js terminal** embedded per-agent, attached to a PTY exposed by
   the harness. Pairs well with the unprivileged-container work — would let
   the operator drop into the container without `nixos-container root-login`.