Weather forecast page, 16 elements per page, attribute paths, examples from the display

- Home Assistant attributes can be paths into lists (forecast.1.condition).
- Date elements can show a day ahead (day offset 0-7).
- Pages hold 16 elements (page format 6; the old formats are frozen at 8).
  Pages are reset in place (clearPage), not through a 4 KB temporary.
- Verwachting page: today (icon, temperature, max/min) and the next 2
  days with 7 x 7 icons (weer7 <condition>), from a template sensor
  (docs/home-assistant.md).
- examples/home-pages.json is exported from the display with all pages
  and their icons, private entity id parts replaced by placeholders
  (tools/export_examples.py replaces tools/make_example_pages.py).

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

src/esp32/logic/page.cpp

@@ -127,7 +127,7 @@ static bool strncasecmpAscii(const char *a, const char *b, size_t n)
 static bool validAttribute(const char *attribute)
 {
 	for (const char *c = attribute; *c; c++)
-		if (!isalnum((unsigned char)*c) && *c != '_')
+		if (!isalnum((unsigned char)*c) && *c != '_' && *c != '.') // dots: a path, e.g. forecast.1.condition
 			return false;
 	return true;
 }
@@ -196,6 +196,8 @@ const char *validatePage(const DynamicPage &page)
 			return "The list of texts can only contain plain characters, up to 63";
 		if (e.format >= formatCount(e))
 			return "Unknown format";
+		if (e.day_offset < 0 || e.day_offset > DAY_OFFSET_MAX)
+			return "Date: 0-7 days after today";
 		if (!isfinite(e.factor) || e.factor == 0)
 			return "The multiplier must be a number other than 0";
 		if (e.scroll_width > 2 * BITMAP_WIDTH ||
@@ -368,8 +370,37 @@ static int language(const PageElement &e)
 	return e.language < Language::Count ? (int)e.language : 0;
 }
 
-static void formatDate(const PageElement &e, const LocalTime &t, char *out, size_t size)
+static int daysInMonth(int year, int month)
 {
+	static const int DAYS[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
+	bool leap = (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
+	return month == 2 && leap ? 29 : DAYS[(month - 1 + 12) % 12];
+}
+
+LocalTime addDays(const LocalTime &time, int days)
+{
+	LocalTime t = time;
+	if (t.month < 1 || t.month > 12)
+		return t;
+	for (int i = 0; i < days; i++)
+	{
+		t.weekday = (t.weekday + 1) % 7;
+		if (++t.day > daysInMonth(t.year, t.month))
+		{
+			t.day = 1;
+			if (++t.month > 12)
+			{
+				t.month = 1;
+				t.year++;
+			}
+		}
+	}
+	return t;
+}
+
+static void formatDate(const PageElement &e, const LocalTime &today, char *out, size_t size)
+{
+	LocalTime t = addDays(today, e.day_offset);
 	int lang = language(e);
 	int wd = t.weekday >= 0 && t.weekday < 7 ? t.weekday : 0;
 	int mo = t.month >= 1 && t.month <= 12 ? t.month - 1 : 0;