Phase 6: procedural LVGL canvas icons + manual retry on weather tile

- src/icons/icons.{h,cpp}: colored procedural icons drawn onto LVGL
  canvases (PSRAM-backed ARGB8888): sun, moon, cloud, rain, thunderstorm
  (selected from API symbol field), rain-warning triangle, retry/error
  symbol, back arrow. Replaces old M5GFX-based icons.h.
- tile_button: add tile_button_set_icon_obj() to swap text glyph for a
  canvas icon object
- home_screen: weather tile now shows the real procedural weather icon
  (rebuilt on each refresh); tapping the weather tile in error state
  triggers a manual retry (SPEC.md section 8) instead of navigating

src/ui/home_screen.cpp

@@ -1,5 +1,6 @@
 #include "home_screen.h"
 #include "ui/widgets/tile_button.h"
+#include "icons/icons.h"
 #include "api/weather_api.h"
 #include "api/calendar_api.h"
 #include <theme.h>
@@ -12,7 +13,10 @@ namespace {
 // --- navigation callback target (set by main.cpp) ---
 ScreenId (*g_navigate)(ScreenId) = nullptr;
 
-void on_weather_tile(lv_event_t *) { if (g_navigate) g_navigate(ScreenId::WEATHER_DETAIL); }
+// Forward declarations (definitions below).
+void updateWidgets();
+void doFetch();
+
 void on_calendar_tile(lv_event_t *) { if (g_navigate) g_navigate(ScreenId::CALENDAR_DETAIL); }
 void on_mvg_tile(lv_event_t *) { if (g_navigate) g_navigate(ScreenId::MVG); }
 
@@ -30,6 +34,13 @@ TileButton calendarTile{};
 TileButton mvgTile{};
 bool widgetsBuilt = false;
 
+// Rebuild the weather canvas icon (deleted + recreated on each refresh
+// because the symbol may change).
+void rebuildWeatherIcon(const String &symbol, const String &description) {
+    lv_obj_t *ic = Icons::createWeatherIcon(weatherTile.btn, symbol, description, 48);
+    tile_button_set_icon_obj(weatherTile, ic);
+}
+
 void doFetch() {
     WeatherData w = fetchWeather();
     weatherOk = w.valid;
@@ -40,13 +51,23 @@ void doFetch() {
     lastFetchMs = millis();
 }
 
+// Manual retry: tapping the weather tile when it is in error state triggers
+// a refresh instead of navigating away. Acts as the SPEC.md "retry per tap".
+void on_weather_tile(lv_event_t *e) {
+    if (!weatherOk) {
+        doFetch();
+        updateWidgets();
+        return;
+    }
+    if (g_navigate) g_navigate(ScreenId::WEATHER_DETAIL);
+}
+
 // --- formatting helpers (ported from old home_screen.cpp rendering) ---
 
 String weatherIconGlyph(const String &symbol) {
-    // Phase 4 placeholder: map symbol condition to a unicode glyph until
-    // bitmap icons land in Phase 6. m=night, condition char = symbol[1].
+    // Kept for fallback; real icons are drawn as canvas via rebuildWeatherIcon.
     (void)symbol;
-    return LV_SYMBOL_IMAGE; // cloud/weather placeholder; bitmaps come in Phase 6
+    return LV_SYMBOL_IMAGE;
 }
 
 String formatWeatherValue(const WeatherData &w) {
@@ -75,7 +96,7 @@ String formatCalendarPreview(const CalendarData &c) {
 void updateWidgets() {
     if (!widgetsBuilt) return;
     tile_button_set_value(weatherTile, formatWeatherValue(lastWeather).c_str());
-    tile_button_set_icon(weatherTile, weatherIconGlyph(lastWeather.current.symbol).c_str());
+    rebuildWeatherIcon(lastWeather.current.symbol, lastWeather.current.description);
     tile_button_set_value(calendarTile, formatCalendarPreview(lastCalendar).c_str());
     tile_button_set_icon(calendarTile, LV_SYMBOL_FILE);
     tile_button_set_value(mvgTile, "");

src/ui/widgets/tile_button.cpp

@@ -48,3 +48,9 @@ void tile_button_set_value(TileButton &t, const char *text) {
 void tile_button_set_icon(TileButton &t, const char *text) {
     if (t.icon) lv_label_set_text(t.icon, text);
 }
+
+void tile_button_set_icon_obj(TileButton &t, lv_obj_t *icon_obj) {
+    if (t.icon) lv_obj_del(t.icon);
+    t.icon = icon_obj;
+    if (t.icon) lv_obj_align(t.icon, LV_ALIGN_TOP_RIGHT, 0, 0);
+}

src/ui/widgets/tile_button.h

@@ -24,3 +24,7 @@ void tile_button_set_value(TileButton &t, const char *text);
 // Set the icon text (single glyph/symbol). Icons are rendered as text labels
 // using LVGL's built-in font until bitmap icons land in Phase 6.
 void tile_button_set_icon(TileButton &t, const char *text);
+
+// Replace the text icon with an already-created canvas object (the caller
+// creates the canvas as a child of t.btn). Useful for bitmap/procedural icons.
+void tile_button_set_icon_obj(TileButton &t, lv_obj_t *icon_obj);