Restructure ESP32 firmware into modules, fix bugs, add tests

Structure (src/esp32/):
- logic/: DisplayController, schedule, power timer, LED pattern; pure C++
- display/: FlipdotFrames and bitmaps
- nano_link/: NanoLink (relay, serial, READY, bootloader) and flash bridge
- net/: WiFi/OTA/panic window, Home Assistant
- config.h with all settings; libs.h (globals in a header) removed

Bug fixes:
- Home Assistant switches now report their state back and start as ON
- loop() no longer blocks: WiFi.waitForConnectResult() (up to 60 s
  without WiFi) and getLocalTime() (5 s before NTP sync) were called
  every iteration
- Power switch off now powers off after 1 s even when a 30 s countdown
  is already running
- millis() overflow safe power-off timer; no frame catch-up bursts
- No garbage time string before NTP sync; 'Connecting...' stays instead
- Frames are only sent when the screen changes instead of every second
- Reset reasons are logged once instead of every 100 ms
- Removed dead code (unused fonts, WiFiMulti, rotated bitmap, ...)

Tests: new test_esp32 environment (26 tests); native renamed to test_nano

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/esp32/display/frames.cpp

@@ -0,0 +1,55 @@
+#include "display/frames.h"
+
+#include <stdio.h>
+
+#include "display/bitmaps.h"
+#include "logic/schedule.h"
+
+// Horizontal offset that centers the 81 pixel wide clock on the 84 pixel display
+static const int CLOCK_X = 3;
+
+FlipdotFrames::FlipdotFrames(BROSE9323 &display) : _display(display)
+{
+}
+
+void FlipdotFrames::clock(int hour, int minute)
+{
+	char time[6];
+	snprintf(time, sizeof(time), "%02d:%02d", hour, minute);
+
+	_display.fillScreen(0);
+	if (isEvening(hour))
+		_display.drawBitmap(CLOCK_X, 0, yawning_pikachu_bitmap_yawning_pikachu_black_border, 35, 19, 1);
+	else
+		_display.drawBitmap(CLOCK_X, 0, pikachu_bitmap_pikachu_black_border, 35, 19, 1);
+	_display.drawBitmap(CLOCK_X + 35, 0, clock_thought_bubble_bitmap_clock_thought_bubble, 46, 19, 1);
+
+	_display.setTextSize(1);
+	_display.setTextWrap(false);
+	_display.setCursor(CLOCK_X + 43, 4);
+	_display.print(time);
+	_display.display();
+}
+
+void FlipdotFrames::logo()
+{
+	_display.fillScreen(0);
+	_display.drawBitmap(0, 0, nintendo_bitmap_Nintendo_new, 84, 19, 1);
+	_display.display();
+}
+
+void FlipdotFrames::blank()
+{
+	_display.fillScreen(0);
+	_display.display();
+}
+
+void FlipdotFrames::message(const char *text)
+{
+	_display.fillScreen(0);
+	_display.setTextSize(1);
+	_display.setTextWrap(true);
+	_display.setCursor(0, 0);
+	_display.print(text);
+	_display.display();
+}