polish(v0.6): redesign Sessions/Projects toggle + hide keybar on home

- Segmented control: replace the two free-standing bordered boxes with a
  single rounded track holding two pill buttons (iOS-style), active segment
  filled Amber; centred via fit-content + margin auto. Panel top-offset 44→68px.
- Hide the bottom key-bar on the home chooser (it only targets an active
  terminal): updateHomeView toggles body.home-open; CSS hides #keybar.

Frontend-only. 415 tests green; both typechecks clean; verified in-browser
(toggle pill renders, keybar hidden on home, reappears when a tab opens).

public/tabs.ts

@@ -122,6 +122,10 @@ export class TabApp {
     // The ⌂ button is "pressed" only while overlaying home on top of open tabs.
     this.homeBtn?.classList.toggle('active', this.homeForced && this.tabs.length > 0)
 
+    // Hide the bottom key-bar on the home chooser — it only sends keys to an
+    // active terminal, so it's noise on the Sessions/Projects views.
+    document.body.classList.toggle('home-open', showHome)
+
     if (showHome) {
       // Overlay home: hide every terminal pane so the chooser is on top.
       for (const t of this.tabs) t.session.hide()