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.

app/schemas/pricingPlanSchema.ts

@@ -0,0 +1,57 @@
+import { z } from "zod";
+import { ButtonPropsSchema } from "./buttonSchema";
+
+/**
+ * Zod schema for UPricingPlan component (basic props only)
+ * Reference: https://ui.nuxt.com/docs/components/pricing-plan#props
+ */
+export const PricingPlanPropsSchema = z.object({
+  /** The title of the pricing plan. */
+  title: z.string(),
+  /** The description text shown under the title. */
+  description: z.string().optional(),
+  /** The current price of the plan. */
+  price: z.string().optional(),
+  /**
+   * Discounted price.
+   * When set, the main price will appear with a strikethrough.
+   */
+  discount: z.string().optional(),
+  /** The unit period (e.g. /month) displayed next to price. */
+  billingCycle: z.string().optional(),
+  /** Additional billing text above the billing cycle. */
+  billingPeriod: z.string().optional(),
+  /**
+   * List of plan features.
+   * Can be an array of strings or array of objects (feature items).
+   */
+  features: z.array(z.string()).optional().default([]),
+  /** The button displayed at the bottom (ButtonProps). */
+  button: ButtonPropsSchema.optional(),
+  /**
+   * Visual variant of the pricing plan.
+   * @default "outline"
+   */
+  variant: z.enum(["soft", "solid", "outline", "subtle"]).optional().default("outline"),
+  /**
+   * Layout orientation of the component.
+   * @default "vertical"
+   */
+  orientation: z.enum(["vertical", "horizontal"]).optional().default("vertical"),
+  /** Optional tagline text displayed above price. */
+  tagline: z.string().optional(),
+  /** Terms or disclaimer text displayed below features. */
+  terms: z.string().optional(),
+  /**
+   * Highlights the pricing plan visually (adds a ring around it).
+   * @default false
+   */
+  highlight: z.boolean().optional().default(false),
+  /**
+   * Enlarges the plan card slightly for emphasis.
+   * @default false
+   */
+  scale: z.boolean().optional().default(false),
+});
+
+export type PricingPlanProps = z.infer<typeof PricingPlanPropsSchema>;