polish(v0.6): make "New session" a grid tile instead of a heavy header button

The big solid-amber "+ New session" button clashed with the refined segmented
control. Replace it with a dashed "+" tile that leads the session grid (same
size as the session cards, re-prepended each refresh), so it reads as a natural
"create" cell. Header is now just the title + Sessions/Projects toggle; the
redundant empty-state message is gone (the tile is the CTA).

Frontend-only (launcher.ts + style.css). Verified: web typecheck + build clean,
preview-grid tests green, in-browser the grid leads with the New-session tile
followed by the session cards (Open/Kill).

public/launcher.ts

@@ -42,16 +42,20 @@ export function mountLauncher(host: HTMLElement, hooks: LauncherHooks): Launcher
   const head = el('div', 'launcher-head')
   head.append(el('div', 'launcher-title', 'Your sessions'))
   const sub = el('div', 'launcher-sub', '')
-  const actions = el('div', 'launcher-actions')
-  const newBtn = el('button', 'launcher-new', '＋ New session')
-  newBtn.addEventListener('click', () => hooks.onNew())
-  actions.append(newBtn)
-  head.append(sub, actions)
+  head.append(sub)
   root.append(head)
 
   const grid = el('div', 'mg-grid')
   root.append(grid)
 
+  // "New session" is a tile that leads the grid (matches the session cards),
+  // instead of a heavy header button. Re-prepended on every refresh.
+  const newTile = el('button', 'mg-new-card')
+  newTile.title = 'Start a new session'
+  newTile.setAttribute('aria-label', 'New session')
+  newTile.append(el('div', 'mg-new-plus', '＋'), el('div', 'mg-new-label', 'New session'))
+  newTile.addEventListener('click', () => hooks.onNew())
+
   const cards = new Map<string, PreviewCard>()
   let timer: ReturnType<typeof setInterval> | null = null
 
@@ -78,6 +82,9 @@ export function mountLauncher(host: HTMLElement, hooks: LauncherHooks): Launcher
       ? `${sessions.length} running on this host — pick one to open`
       : 'No sessions running yet'
 
+    // Keep the New-session tile as the first grid cell.
+    if (grid.firstChild !== newTile) grid.prepend(newTile)
+
     const seen = new Set<string>()
     for (const s of sessions) {
       seen.add(s.id)
@@ -99,10 +106,6 @@ export function mountLauncher(host: HTMLElement, hooks: LauncherHooks): Launcher
       }
     }
 
-    grid.querySelector('.mg-empty')?.remove()
-    if (sessions.length === 0) {
-      grid.append(el('div', 'mg-empty', 'No running sessions. Click “New session” to start one.'))
-    }
   }
 
   return {