feat(agent): Pi in-app agent with tool router

New Pi tab. Talks to a typed tool router that maps natural-language
intent to real EA2 calls:

  navigate         go to mission / runs / studio / chat / hubs
  start_process    'run laptop procurement for store-204'
  send_chat        'tell Mariana that the quote is approved'
  create_process   opens the wizard
  list_processes   pulls published flow definitions for the tenant

This is the OSS-pluggable shape: today the router is rule-based and
fully wired to FlowMaster; swapping in an LLM provider for intent
parsing is a localised change in routeAgentInput().

src/App.tsx

@@ -9,6 +9,7 @@ import Settings from "./scenes/Settings";
 import Login from "./scenes/Login";
 import SsoCallback from "./scenes/SsoCallback";
 import Chat from "./scenes/Chat";
+import Agent from "./scenes/Agent";
 import CommandBar from "./components/CommandBar";
 import Toaster from "./components/Toaster";
 import Console from "./components/Console";
@@ -75,6 +76,9 @@ export default function App() {
             <button role="tab" aria-selected={scene === "chat"} className={`tab${scene === "chat" ? " tab-sel" : ""}`} onClick={() => setScene("chat")}>
               <Bot size={13} /> Chat
             </button>
+            <button role="tab" aria-selected={scene === "agent"} className={`tab${scene === "agent" ? " tab-sel" : ""}`} onClick={() => setScene("agent")}>
+              <Bot size={13} /> Pi
+            </button>
             <button role="tab" aria-selected={scene === "settings"} className={`tab${scene === "settings" ? " tab-sel" : ""}`} onClick={() => setScene("settings")}>
               <Cog size={13} /> Settings
             </button>
@@ -154,6 +158,7 @@ export default function App() {
         {scene === "history" && <RunHistory />}
         {scene === "studio" && <Wizard />}
         {scene === "chat" && <Chat />}
+        {scene === "agent" && <Agent />}
         {scene === "settings" && <Settings />}
       </div>