feat(webDev): add inquiry modal for pricing plans

This commit introduces a 'Contact Sales' modal on the web development page, allowing users to inquire about specific service plans.

- The pricing plan buttons now trigger this modal, pre-filled with the selected plan's details.
- Users can add custom remarks to their inquiry.
- On submission, a pre-formatted message is generated and opened in WhatsApp using a new `useWhatsAppMsgSender` composable.
- Adds `NUXT_PUBLIC_WHATSAPP_NUMBER` to the runtime configuration.
- Refactors content validation by introducing Zod schemas for `PricingPlan` and `Button` props to improve type safety.
- Adds new i18n keys for the modal interface and message templates.

i18n/locales/en-US/common.json

@@ -52,6 +52,11 @@
           }
         }
       }
+    },
+    "button": {
+      "cancel": "Cancel",
+      "submit": "Submit",
+      "saving": "Saving..."
     }
   }
 }