Add conversions for Home Assistant values: duration, time, own texts, auto unit

- Show as number (multiplier, decimals, auto unit W -> kW -> MW, without
  minus sign), duration (seconds/minutes/hours as 2h 21m, 2:21:00, 2:21 or
  smart), time (HA timestamps in local time, with weekday or date, or
  relative: over 34 min / 12 min geleden) or own texts per state.
- Page format 3; version 2 pages are converted. Version 2.7.0.

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

src/esp32/web/page_json.h

@@ -9,7 +9,9 @@
 //    elements: [{type: "clock"|"date"|"ha"|"text", x, y, align: "left"|"center"|"right",
 //                overlay: "top"|"box"|"invert", font, format, language: "nl"|"en",
 //                decimals (-1 = as received), text, suffix, entity, attribute, factor,
-//                scroll_width, scroll_speed, target ("YYYY-MM-DDTHH:MM")}]}
+//                scroll_width, scroll_speed, target ("YYYY-MM-DDTHH:MM"),
+//                show: "number"|"duration"|"time"|"map", input_unit: "s"|"min"|"h",
+//                auto_unit, absolute, map}]}
 //   type also "countdown", "stopwatch", "image". Texts use the UTF-8 degree sign.
 
 void pageToJson(const DynamicPage &page, JsonObject out);