Add missing admin translations for Fixed Price field

Updated all translation files with new strings from v1.1.4:
- Simplified "How to calculate the price" description
- New "Fixed Price" field label
- New "Enter the fixed price for this composable product" description

Translations added to all 6 locales:
- de_DE (German formal): Festpreis / Geben Sie den Festpreis ein
- de_DE_informal (German informal): Festpreis / Gib den Festpreis ein
- de_CH (Swiss German formal): Festpreis / Geben Sie den Festpreis ein
- de_CH_informal (Swiss German informal): Festpreis / Gib den Festpreis ein
- fr_CH (Swiss French): Prix fixe / Entrez le prix fixe
- it_CH (Swiss Italian): Prezzo fisso / Inserisci il prezzo fisso

All admin strings are now fully translated across all supported locales.

Updated CLAUDE.md "Bugs found" section to mark admin translation task as completed.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

languages/wc-composable-product-it_CH.po

@@ -144,8 +144,16 @@ msgid "Pricing Mode"
 msgstr "Modalità di prezzo"
 
 #: includes/Admin/Product_Data.php
-msgid "How to calculate the price. Leave empty to use global default."
-msgstr "Come calcolare il prezzo. Lasciare vuoto per utilizzare il valore predefinito globale."
+msgid "How to calculate the price."
+msgstr "Come calcolare il prezzo."
+
+#: includes/Admin/Product_Data.php
+msgid "Fixed Price"
+msgstr "Prezzo fisso"
+
+#: includes/Admin/Product_Data.php
+msgid "Enter the fixed price for this composable product."
+msgstr "Inserisci il prezzo fisso per questo prodotto componibile."
 
 #: includes/Admin/Product_Data.php
 msgid "Use global default"