feat(hubs): Procurement / People / IT hubs over real EA2 catalogue

Single Hub component parameterised by hub key. Each hub:
- Lists quick actions that look up a matching published process and
  start it as a real transaction
- Pulls the full published catalogue from /api/ea2/flow/processes and
  filters via a hub-specific regex (procurement|hr|it)
- Falls back to top-N when no matches, with a Studio CTA when empty

Landing surface gets a hero-hub row of chips: Procurement Hub, People
Hub, IT Hub, Talk to Pi, Team Chat. Same EA2-write doctrine as wizard.

src/scenes/Landing.tsx

@@ -75,6 +75,14 @@ export default function Landing() {
             </button>
           </div>
 
+          <div className="hero-hub-row">
+            <button className="hub-chip" onClick={() => setScene("hub-procurement")}>Procurement Hub</button>
+            <button className="hub-chip" onClick={() => setScene("hub-hr")}>People Hub</button>
+            <button className="hub-chip" onClick={() => setScene("hub-it")}>IT Hub</button>
+            <button className="hub-chip" onClick={() => setScene("agent")}>Talk to Pi</button>
+            <button className="hub-chip" onClick={() => setScene("chat")}>Team Chat</button>
+          </div>
+
           <div className="hero-stats">
             <div className="stat">
               <Pulse size={12} />