[select][lvgl] Fix FixedVector size() returning 0 when using operator[] after init() (#11721)

esphome/components/lvgl/select/lvgl_select.h

@@ -59,8 +59,8 @@ class LVGLSelect : public select::Select, public Component {
     const auto &opts = this->widget_->get_options();
     FixedVector<const char *> opt_ptrs;
     opt_ptrs.init(opts.size());
-    for (size_t i = 0; i < opts.size(); i++) {
-      opt_ptrs[i] = opts[i].c_str();
+    for (const auto &opt : opts) {
+      opt_ptrs.push_back(opt.c_str());
     }
     this->traits.set_options(opt_ptrs);
   }

esphome/components/select/select_traits.cpp

@@ -7,8 +7,8 @@ void SelectTraits::set_options(const std::initializer_list<const char *> &option
 
 void SelectTraits::set_options(const FixedVector<const char *> &options) {
   this->options_.init(options.size());
-  for (size_t i = 0; i < options.size(); i++) {
-    this->options_[i] = options[i];
+  for (const auto &opt : options) {
+    this->options_.push_back(opt);
   }
 }
 

esphome/core/helpers.h

@@ -248,6 +248,8 @@ template<typename T> class FixedVector {
   }
 
   // Allocate capacity - can be called multiple times to reinit
+  // IMPORTANT: After calling init(), you MUST use push_back() to add elements.
+  // Direct assignment via operator[] does NOT update the size counter.
   void init(size_t n) {
     cleanup_();
     reset_();