[esp32] Preserve crash data across OTA rollback reboots

Don't clear the crash data magic marker at boot time. Previously,
crash_handler_read_and_clear() would clear the magic immediately,
so if OTA rollback triggered a reboot before an API client connected,
the crash trace was lost.

Now the magic is only cleared after crash_handler_log() delivers the
data to an API client via crash_handler_clear().

esphome/components/api/api_connection.h

@@ -276,6 +276,7 @@ class APIConnection final : public APIServerConnectionBase {
       App.schedule_dump_config();
 #ifdef USE_ESP32_CRASH_HANDLER
     esp32::crash_handler_log();
+    esp32::crash_handler_clear();
 #endif
 #ifdef USE_RP2040_CRASH_HANDLER
     rp2040::crash_handler_log();

esphome/components/esp32/crash_handler.cpp

@@ -101,12 +101,17 @@ void crash_handler_read_and_clear() {
     if (s_raw_crash_data.pseudo_excause > 1)
       s_raw_crash_data.pseudo_excause = 0;
   }
-  // Clear magic regardless so we don't re-report on next normal reboot
-  s_raw_crash_data.magic = 0;
+  // Don't clear magic here — crash data must survive OTA rollback reboots.
+  // Magic is cleared by crash_handler_clear() after an API client receives the data.
 }
 
 bool crash_handler_has_data() { return s_crash_data_valid; }
 
+void crash_handler_clear() {
+  s_raw_crash_data.magic = 0;
+  s_crash_data_valid = false;
+}
+
 // Look up the exception cause as a human-readable string.
 // Tables mirror ESP-IDF's panic_arch_fill_info() which uses local static arrays
 // not exposed via any public API.

esphome/components/esp32/crash_handler.h

@@ -4,12 +4,18 @@
 
 namespace esphome::esp32 {
 
-/// Read crash data from NOINIT memory and clear the magic marker.
+/// Read and validate crash data from NOINIT memory.
+/// Does not clear the magic marker — call crash_handler_clear() after
+/// the data has been delivered to an API client so it survives OTA rollback reboots.
 void crash_handler_read_and_clear();
 
 /// Log crash data if a crash was detected on previous boot.
 void crash_handler_log();
 
+/// Clear the magic marker and mark crash data as consumed.
+/// Call after the data has been delivered to an API client.
+void crash_handler_clear();
+
 /// Returns true if crash data was found this boot.
 bool crash_handler_has_data();