Add Russian translations and pronunciation button

- Russian fields on Mineral model (name_ru, description_ru, history_ru, etc.)
- scrape_minerals_ru management command fetches from Russian Wikipedia via langlinks
- EN/RU toggle in header, saved to localStorage
- Speaker button next to mineral name uses Web Speech API
- Section headers and labels translated
- Russian Wikipedia link in footer when in RU mode

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dailystone/models.py

@@ -18,6 +18,13 @@ class Mineral(models.Model):
     wikipedia_url = models.URLField(max_length=500, blank=True)
     day_of_year = models.IntegerField(unique=True, null=True, blank=True)
 
+    # Russian translations
+    name_ru = models.CharField(max_length=200, blank=True)
+    description_ru = models.TextField(blank=True)
+    history_ru = models.TextField(blank=True)
+    color_description_ru = models.CharField(max_length=300, blank=True)
+    wikipedia_url_ru = models.URLField(max_length=500, blank=True)
+
     class Meta:
         ordering = ['day_of_year']