fix(layout): reserve growable tree vectors up front to avoid bad_alloc

Reserve nodes/specs/styles/labelAt/labels at reset() while the heap still
has a large contiguous block. A doubling realloc mid-build needs old+new
buffers live at once and throws bad_alloc on the heap the build itself has
fragmented; the styles vector was the one tripping the firmware's global
new-handler into a reset with ~10 populated cards.

UNVALIDATED: reproduced and fixed in the emulator only. Hardware has ~30KB
less free (NimBLE DMA buffers), so the reserves at reset() may still be
marginal there -- not yet tested on the board.

native/include/lua/layout.h

@@ -144,7 +144,10 @@ public:
   // Growth doubling needs the old and new buffers live at once, which is the
   // allocation that fails first on a tight heap. One reservation covers a
   // typical screen so a build reallocates only if it genuinely gets large.
-  static constexpr size_t RESERVE = 64;
+  // 512 skips most growth-doubling reallocs during a build (a typical screen is
+  // ~300 nodes); 64 forced 4-5 doubling moves, each fragmenting the heap while
+  // old and new buffers are both live.
+  static constexpr size_t RESERVE = 512;
 
   void reset() {
     focus = NONE;
@@ -156,6 +159,14 @@ public:
     labels.clear();
     styles.clear();
     scrollState.clear();
+    // Reserve every growable vector while the heap still has a large contiguous
+    // block. A doubling realloc mid-build needs old+new live at once and throws
+    // bad_alloc on a heap the build has already fragmented -- the styles vector
+    // is what the global new-handler caught and turned into a reset. styles is
+    // sparser than nodes; labels is a byte arena.
+    labelAt.reserve(RESERVE);
+    styles.reserve(RESERVE / 2);
+    labels.reserve(1024);
     error = nullptr;
   }