build: shrink bootloader to fit iram

Log level INFO pulls libc printf into IRAM (~15 KB), overflowing
the fixed 12 KB iram_seg by 9787 bytes. Pin SIZE optimization
and drop to WARN level to avoid the vfprintf/stdio chain.

sdkconfig.defaults

@@ -10,6 +10,14 @@ CONFIG_PARTITION_TABLE_CUSTOM_FILENAME="partitions.csv"
 CONFIG_LOG_DEFAULT_LEVEL_INFO=y
 CONFIG_COMPILER_OPTIMIZATION_PERF=y
 
+# --- Bootloader size: keep the 2nd-stage bootloader inside iram_seg ----------
+# Without these the bootloader links at -O2 (PERF) and pulls in the full
+# libc printf machinery (svfiprintf ~9 KB) which overflows the 12 KB iram_seg.
+# SIZE (-Os) reduces code but alone is not sufficient; dropping the log level
+# from INFO to WARN removes the format-string I/O paths that pull libc stdio.
+CONFIG_BOOTLOADER_COMPILER_OPTIMIZATION_SIZE=y
+CONFIG_BOOTLOADER_LOG_LEVEL_WARN=y
+
 # --- FreeRTOS ----------------------------------------------------------------
 # 1 kHz tick gives smoother LVGL animations (bubble breathing, transitions).
 CONFIG_FREERTOS_HZ=1000