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/style.css

@@ -711,18 +711,35 @@ body {
   display: flex;
   gap: 8px;
 }
-.launcher-new {
-  background: var(--accent);
-  color: var(--on-accent);
-  border: none;
-  border-radius: 8px;
-  padding: 9px 16px;
-  font: inherit;
-  font-weight: 600;
+/* "New session" tile — leads the session grid, matching the session cards. */
+.mg-new-card {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  gap: 8px;
+  min-height: 200px;
+  background: none;
+  border: 2px dashed var(--border-strong);
+  border-radius: 12px;
+  color: var(--text-dim);
   cursor: pointer;
+  font: inherit;
+  transition: border-color 0.12s ease, color 0.12s ease, background 0.12s ease;
 }
-.launcher-new:hover {
-  background: var(--accent-2);
+.mg-new-card:hover {
+  border-color: var(--accent);
+  color: var(--accent);
+  background: var(--accent-soft);
+}
+.mg-new-plus {
+  font-size: 34px;
+  font-weight: 300;
+  line-height: 1;
+}
+.mg-new-label {
+  font-size: 14px;
+  font-weight: 600;
 }
 
 /* ── Session Manager page (manage.html) ──────────────────────────── */