docs sync + revert auto-unfree removal

revert the earlier 'operator must set allowUnfree' move:
per-agent containers evaluate their own nixpkgs and the operator's
host-level allowUnfree doesn't propagate in. restoring the scoped
allowUnfreePredicate inside both the claude-unstable overlay and
harness-base.nix; documented in README + gotchas as 'nothing to
set on the operator side'.

docs:
- claude.md file map adds crash_watch.rs, kick_agent on coordinator,
  /api/model + journald viewer + bind-with-retry references.
- scratchpad rewritten to reflect the recent run.
- web-ui.md: notification row + browser notifications section,
  state row (badge + model chip + last-turn chip + cancel button),
  per-agent inbox, /model slash, /cancel-question + journald
  endpoints, focus-preservation on refresh.
- turn-loop.md: --model is read from Bus::model() per turn (runtime
  override via /model); recv(wait_seconds) up to 180s with the
  rationale; ask_operator gains ttl_seconds; new TurnState section;
  kick_agent inbox-on-startup hint.
- approvals.md: ttl/cancel resolution paths for operator questions.
- persistence.md: /state/hyperhive-model file.
- gotchas.md: web UI port collision policy (rename, don't probe);
  bind retry + SO_REUSEADDR shape; auto-unfree restored.
- todo.md: cleaned up empty sections and stale entries; /model
  shipped, dropped from the list.

nix/templates/harness-base.nix

@@ -7,12 +7,11 @@
 
   boot.isNspawnContainer = true;
 
-  # `claude-code` is unfree. hyperhive intentionally does NOT auto-allow
-  # it — the operator opts in by setting
-  # `nixpkgs.config.allowUnfreePredicate` (or `allowUnfree = true`) in
-  # their own host config / agent.nix. Without that, the per-agent
-  # build fails on this package and the operator sees an honest "this
-  # is unfree, are you sure?" error.
+  # `claude-code` is unfree. Each per-agent container's nixosConfiguration
+  # evaluates its own `nixpkgs` instance, so the operator's host-level
+  # `nixpkgs.config.allowUnfreePredicate` does not propagate into here —
+  # we have to allow it inside the container's config as well.
+  nixpkgs.config.allowUnfreePredicate = pkg: builtins.elem (pkgs.lib.getName pkg) [ "claude-code" ];
 
   environment.systemPackages = with pkgs; [
     hyperhive