Redesign web UI with console-style squircle message cards

Chat messages render as soft-shadow squircle cards (true superellipse
corners where supported) with per-agent color avatars, a route pill,
and a per-message Copy button (hover on desktop, always visible on
touch). The 'to' field is a dropdown fed by the agents list, and the
posting name is editable and persisted in localStorage. Setup tab
matches the same look with a copyable install command.

test/api.test.ts

@@ -114,6 +114,8 @@ describe("web pages", () => {
     const chat = await (await handle(new Request("http://chat.example.com/chat"))).text();
     expect(chat).toContain('id="send"');
     expect(chat).toContain('id="clear"');
+    expect(chat).toContain('id="to"');
+    expect(chat).toContain('id="myname"');
   });
 });