Add a page schedule with rotation, Home Assistant trigger rules and a Stopwatch tab

- Schedule: daily blocks from a start time, each with up to 6 rotating pages
  or bitmaps (own duration), switching with the effect or instantly. A manual
  pick (Show tab, HA Mode) lasts until the next block; Back to schedule ends it.
- Rules: an HA state (=, is not, above, below) shows a page while true, adds it
  to the rotation while true, or shows it for N seconds when it becomes true.
  Each rule is polled at its own interval, with a 60 s back-off on errors.
- PageSelector (pure logic, tested) decides the shown page; schedule stored in
  NVS; HA sensor Shown page and button Back to schedule.
- Web UI: Schedule and Stopwatch tabs, bitmaps used by pages or rules in their
  own subsection, schedule in export/import. Version 2.6.0.

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

src/esp32/net/home_assistant.cpp

@@ -30,6 +30,8 @@ static HASensor ipSensor("FlipDotDisplayIP");
 static HAButton recoveryButton("FlipDotDisplayRecovery");
 static HASwitch stopwatchSwitch("FlipDotDisplayStopwatch");
 static HAButton stopwatchReset("FlipDotDisplayStopwatchReset");
+static HASensor shownSensor("FlipDotDisplayShownPage");
+static HAButton backButton("FlipDotDisplayBackToSchedule");
 
 // Removed entities: their retained discovery config is cleared, so Home Assistant
 // deletes them instead of showing them as unavailable
@@ -61,6 +63,7 @@ struct TextSensor
 
 static TextSensor firmware = {firmwareSensor, "", false};
 static TextSensor ip = {ipSensor, "", false};
+static TextSensor shownPage = {shownSensor, "", false};
 
 static DisplayController *displayController = nullptr;
 static bool enabled = false;
@@ -233,6 +236,12 @@ void homeAssistantBegin(DisplayController &controller, const HomeAssistantSettin
 	recoveryButton.setIcon("mdi:lifebuoy");
 	recoveryButton.onCommand([](HAButton *) { rebootToRecovery(RecoveryReason::Manual); });
 
+	shownSensor.setName("FlipDot Display Shown page");
+	shownSensor.setIcon("mdi:monitor-eye");
+	backButton.setName("FlipDot Display Back to schedule");
+	backButton.setIcon("mdi:calendar-clock");
+	backButton.onCommand([](HAButton *) { appBackToSchedule(); });
+
 	firmwareSensor.setName("FlipDot Display Firmware");
 	firmwareSensor.setIcon("mdi:chip");
 
@@ -241,6 +250,7 @@ void homeAssistantBegin(DisplayController &controller, const HomeAssistantSettin
 
 	mqtt.onConnected([]() {
 		firmware.sent = false;
+		shownPage.sent = false;
 		ip.sent = false;
 		clearRemovedEntities();
 	});
@@ -271,6 +281,8 @@ void homeAssistantLoop()
 		ip.set(WiFi.localIP().toString().c_str());
 	}
 	ip.loop();
+	shownPage.set(appShownPage());
+	shownPage.loop();
 	firmware.loop();
 	mode.update();
 	offImage.update();