feat(address): Add i18n support for postal code and phone helper texts #229

Summary

Add prebuild, tree-shakeable i18n modules to @techsio/address for localized helper texts in postal code and phone number inputs.

Problem

Currently, FormPostalInput and FormPhoneInput components require consumers to provide their own translated helpText and errorText props. This leads to:

• Duplicated translation effort across consumers
• Inconsistent messaging
• No centralized source of truth for format hints

Proposed Solution

Create separate i18n modules per language that can be imported individually (tree-shakeable):

libs/address/src/
  i18n/
    types.ts         # Shared types
    cs.ts            # Czech translations
    en.ts            # English translations  
    de.ts            # German translations
    index.ts         # Re-exports all (optional)

API Design

import { getPostalHelpText, getPostalErrorText, getPhoneHelpText } from "@techsio/address/i18n/cs"

<FormPostalInput
  countryCode="CZ"
  helpText={getPostalHelpText("CZ")}    // "Formát: XXX XX"
  errorText={getPostalErrorText("CZ")}  // "Neplatné PSČ"
/>

<FormPhoneInput
  helpText={getPhoneHelpText("CZ")}     // "Formát: 777 888 999"
/>

Helper Text Types

Benefits

• Tree-shakeable: Only imported language gets bundled
• Type-safe: Functions are typed, countryCode is validated
• Prebuild: Resolved at build time, no runtime fetching
• Centralized: Single source of truth for all consumers

Countries to Support

Initial: CZ, SK, DE, AT, PL, GB (EU-typical)

Languages to Support

Initial: cs, en, de (expand as needed)

Tasks

• Create libs/address/src/i18n/types.ts with shared types
• Create libs/address/src/i18n/cs.ts with Czech translations
• Create libs/address/src/i18n/en.ts with English translations
• Create libs/address/src/i18n/de.ts with German translations
• Add exports to libs/address/package.json
• Update FormPostalInput and FormPhoneInput stories to demonstrate usage
• Add documentation

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