icons for the swarm's own forge accounts, and a default agent icon

The builder, ci-metrics and review-classifier forge accounts get an avatar: an
icon each in a hexagonal frame, the hyperhive logo when one is missing. The
controller sets them with a short-lived write:user token it mints for the
account, since only an account can set its own avatar.

An agent with no icon of its own shows a default agent icon in the swarm UI, a
robot head in a round frame, instead of the dimmed hyperhive mark.

nix/packages/assets.nix

@@ -10,6 +10,7 @@
 #
 # Output layout:
 #   $out/share/hyperhive/branding/{hyperhive,agent-configs}.{svg,png}
+#   $out/share/hyperhive/branding/service-*.{svg,png} (the swarm services' forge avatars)
 #   $out/share/hyperhive/prompts/{system.md, claude-settings.json}
 #
 # The repo docs/ tree is a SEPARATE derivation (./reference-docs.nix)
@@ -42,6 +43,9 @@ stdenv.mkDerivation {
     rsvg-convert --width 300 --height 300 \
       -o branding/agent-configs.png \
       branding/agent-configs.svg
+    for svg in branding/service-*.svg; do
+      rsvg-convert --width 300 --height 300 -o "''${svg%.svg}.png" "$svg"
+    done
     runHook postBuild
   '';
 

nix/packages/default.nix

@@ -228,6 +228,7 @@ in
   swarm-ui = pkgs.callPackage ./swarm-ui.nix {
     branding-svg = ../../branding/hyperhive.svg;
     branding-svg-maskable = ../../branding/hyperhive-maskable.svg;
+    agent-default-svg = ../../branding/agent-default.svg;
   };
 
   # Bundled browser assets — see ./frontend.nix. Output is

nix/packages/swarm-ui.nix

@@ -2,6 +2,7 @@
   buildNpmPackage,
   branding-svg,
   branding-svg-maskable,
+  agent-default-svg,
   librsvg,
 }:
 
@@ -66,6 +67,8 @@ buildNpmPackage {
     mkdir -p $out
     cp -r packages/swarm-ui/dist/. $out/
     cp ${branding-svg} $out/favicon.svg
+    # What an agent with no icon of its own shows (`AgentIcon.tsx`).
+    cp ${agent-default-svg} $out/agent-default.svg
     rsvg-convert -w 192 -h 192 ${branding-svg} -o $out/icon-192.png
     rsvg-convert -w 512 -h 512 ${branding-svg} -o $out/icon-512.png