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>

README.md

@@ -96,7 +96,9 @@ view of the display: it shows what the dots show right now, updated every 1.5 s.
 |-----|-----------------|
 | **Show** | Choose what the display shows during the day: a dynamic page (e.g. the built-in Clock: Pikachu with the time) or any bitmap. The schedule still decides when the display is on. |
 | **Pages** | Dynamic pages: a background bitmap per time of day (e.g. Pikachu from 00:00, yawning Pikachu from 17:00) with up to 8 elements on top: clock (`08:05`, `8:05`, optionally with seconds), date (7 formats, Dutch or English), Home Assistant value (entity or attribute, text before and after, multiplier, decimals), text, countdown to a date and time (smart `12 dagen` / `5 uur` / `34 min` / `0:45`, days, `12d 04:05`, with seconds; a text when it has passed), stopwatch (start, stop and reset in the Show tab, the editor and Home Assistant) and image (a bitmap at a position, fixed or chosen by a Home Assistant state, e.g. `weather ` + `cloudy`). Texts can scroll in a window at a chosen speed, and can contain the degree sign. Each element has a position (drag it on the preview), alignment, font and overlay (on top, box that clears the dots behind it, inverted). The preview is drawn by the ESP32, so it is exactly what the display shows. Built-in pages can be copied, not changed. Fonts: Small (3x5), Normal (5x7), Large (5x7 doubled), Full height (19 dot digits), and your own: upload a TTF/OTF, choose the height in dots, the browser converts it. |
-| **Bitmaps** | All bitmaps with a preview: show one as the page, send it live, open it in the editor, delete it. The built-in ones (Nintendo, Pikachu, Pikachu yawning) can't be deleted, nor can a bitmap that a page uses as background. |
+| **Schedule** | What is shown when, every day: blocks from a start time until the next block, each with up to 6 pages or bitmaps that rotate (each for its own time, 5 s to 1 hour), switching with the refresh effect or instantly. Rules: a Home Assistant state (entity or attribute, `=`, `is not`, `above`, `below`) that shows a page while it is true, adds it to the rotation while it is true, or shows it for a while when it becomes true; each rule is read at its own interval (2-600 s). A page chosen by hand (Show tab, HA "Mode") is shown until the next block starts; "Back to schedule" ends it earlier. The display schedule (Settings) still decides when the display is on. |
+| **Stopwatch** | Start, stop and reset the stopwatch that pages can show. |
+| **Bitmaps** | All bitmaps with a preview (the ones that pages or rules use in their own subsection): show one as the page, send it live, open it in the editor, delete it. The built-in ones (Nintendo, Pikachu, Pikachu yawning) can't be deleted, nor can a bitmap that a page uses as background. |
 | **Draw / Live** | Draw on an 84 x 19 canvas (click or drag), or load an image: it is converted in the browser (threshold, invert, dithering, fit / fill / stretch). "Show on display now" sends it to the display right away (*live mode*); with "live while drawing" every change appears on the dots. Save it as a bitmap with a name. |
 | **Settings** | Schedule on/off, when the display is on, the late-evening quarter-hour mode, when it switches off; the "No WiFi" screen; the flip time, the pause after each pulse, pulses per dot and the refresh effect (instant, sparkle, wipe, rain, from the middle out, diagonal, spiral, flip all then reveal, push, random; optionally only for small changes like the clock's minutes); test patterns; the status LED. |
 | **Home Assistant** | On/off, broker, port, user, password (changing these restarts the ESP32; an empty broker uses `secrets.h`). The URL and long-lived access token for the values on dynamic pages (REST API, plain http; empty URL: `http://<broker>:8123`). |
@@ -312,6 +314,8 @@ The ESP32 talks to the Nano on **UART2** (`Serial2`, 115200 baud). The ESP32's o
    - `FlipDot Display IP` sensor: the ESP32's IP address.
    - `FlipDot Display Stopwatch` switch and `FlipDot Display Stopwatch reset` button: the
      stopwatch of the dynamic pages.
+   - `FlipDot Display Shown page` sensor: what the display shows now (schedule, rule or
+     chosen page). `FlipDot Display Back to schedule` button: ends a page chosen by hand.
 4. **Nano.** The Nano reads commands from the serial line and updates its frame buffer.
    On `D` it flips only the dots that changed. Every 2 minutes it redraws the whole screen
    to fix dots that did not flip.