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/config.h

@@ -49,6 +49,8 @@ const uint32_t POWER_OFF_DELAY = 30000;
 // timeout (a read blocks loop() for at most about twice this)
 const uint32_t HA_POLL_INTERVAL = 60000;
 const uint32_t HA_HTTP_TIMEOUT = 1500;
+// After a failed read (Home Assistant down) an entity is read again after this at the soonest
+const uint32_t HA_ERROR_INTERVAL = 60000;
 // Moving dynamic pages (scrolling, seconds): the next frame waits until the Nano received
 // this one (characters per ms at NANO_BAUD) and flipped its changed dots, plus a margin
 const uint32_t NANO_CHARS_PER_MS = NANO_BAUD / 10000;
@@ -103,7 +105,7 @@ const uint32_t SETUP_AP_DELAY = 20000;        // open the AP when WiFi fails thi
 const uint32_t WIFI_CONNECT_TIMEOUT = 30000;
 const uint32_t WIFI_RESTART_TIME = 10UL * 60 * 1000;
 
-#define FIRMWARE_VERSION "2.5.0"
+#define FIRMWARE_VERSION "2.6.0"
 
 // Home Assistant device id (do not change: Home Assistant's entities are linked to it)
 const uint8_t HA_DEVICE_ID[] = {0x34, 0x86, 0x5d, 0x3a, 0x08, 0x28};